research article charge density analysis and transport...

Research ArticleCharge Density Analysis and Transport Properties of TTF BasedMolecular Nanowires A DFT Approach

Karuppannan Selvaraju12 and Poomani Kumaradhas1

1Department of Physics Periyar University Salem 636011 India2Department of Physics Kandaswami Kandarrsquos College Velur 638182 India

Correspondence should be addressed to Poomani Kumaradhas kumaradhasyahoocom

Received 22 July 2014 Accepted 13 November 2014

Academic Editor Emilio Munoz-Sandoval

Copyright copy 2015 K Selvaraju and P Kumaradhas This is an open access article distributed under the Creative CommonsAttribution License which permits unrestricted use distribution and reproduction in any medium provided the original work isproperly cited

Thepresent study has been performed to understand the charge density distribution and the electrical characteristics of Au and thiolsubstituted tetrathiafulvalene (TTF) based molecular nanowire A quantum chemical calculation has been carried out using DFTmethod (B3LYP)with the LANL2DZbasis set under various applied electric fields (EFs)Thebond topological analysis characterizesthe terminal AundashS and SndashC bonds as well as all the bonds of central TTF unit of the molecule The variation of electron densityand Laplacian of electron density at the bond critical point of bonds for zero and different applied fields reveal the electron densitydistribution of the molecule The molecular conformation the variation of atomic charges and energy density distribution of themolecule have been analyzed for the various levels of applied EFs The HOMO-LUMO gap calculated from quantum chemicalcalculations has been compared with the value calculated from the density of states The variation of dipole moment due to thepolarization effect and the 119868-119881 characteristics of the molecule for the various applied EFs have been well discussed

1 Introduction

Molecular scale electronics is known as single moleculeelectronics and it is a branch of nanotechnology Mostly itdeals with single molecules or nanoscale collections of singlemolecules which can be used as basic electronic componentsfor fabricating molecular level devices The ultimate aim ofmolecular electronics is miniaturization of electrical circuitsThis can be done by using single molecules which constitutethe smallest stable structures [1ndash4] In the recent yearslarge efforts have been made to understand structural andelectron transport properties of such molecules [5ndash7] whichare currently being used in electronics as interconnectsdiodes switches rectifiers transistors nonlinear compo-nents dielectrics and memories [8ndash11] Generally higherconductivities originate from highly conjugated molecularsystems [12ndash14] Tetrathiafulvalene (TTF) is a heterocyclicorganosulfur compound which has distinctive electricalproperties notably it exhibits a high anisotropic electricalconductivity In addition TTF is a well-known 120587-electron

donor in the field of organic metals [15ndash17] Studies onthis compound contribute to the development of molecularelectronics Bulk TTF itself has unremarkable electrical prop-erties Distinctive properties are however associated withsalts of its oxidized derivatives [15ndash19] The high electricalconductivity of TTF salts can be attributed to its highsymmetry which promotes charge delocalization therebyminimizing columbic repulsions So far several scientificreports have discussed the TTF and its derivatives [20ndash22]However this is the first report exploring the charge densitydistribution bond topological electrostatic and transportproperties of Au and thiol substituted TTF based molecule(Figure 1) under zero bias and various levels of externalapplied EFs Numerous theoretical ideas have been usedto understand the conductivity of molecular wires (one-dimensional systems) The charge density distribution andelectrostatic properties along with the structural informationgive an accurate outline to design highly conducting newmolecules The wave function obtained from high levelab initioDFT calculations coupled with Baderrsquos Quantum

Hindawi Publishing CorporationJournal of NanoscienceVolume 2015 Article ID 806181 12 pageshttpdxdoiorg1011552015806181

2 Journal of Nanoscience

Au AuS

SS

S

S S

219nm

Figure 1 Au and S substituted tetrathiafulvalene (TTF) basedmolecule

theory of atoms inmolecules (AIM) [23 24]makes it possibleto determine the above properties for zero bias and variousapplied EFs

2 Computational Details

Understanding the effect of applied electric field on thestructural and electronic properties of the Au and thiol sub-stituted TTF basedmolecule has been analyzed by optimizingit for the zero and applied fields for both directions [fivebiasing steps plusmn004 plusmn008 plusmn012 plusmn016 and plusmn020VAminus1] Allcalculations in this study have been carried out using densityfunctional theory (DFT) [23ndash27] Gaussian03 program [28]is used throughout all computations Here we have usedLANL2DZ basis set [29] for whole DFT calculation withB3LYP hybrid function to obtain effective core potential andthe detailed description of the effect of heavy metal atomsin the molecule [29ndash31] All geometric optimizations havebeen performed via Berny algorithm in redundant internalcoordinates The self-consistency of noninteractive wavefunction has been performed with a requested convergenceon the density matrix of 10minus8 and 10minus6 for the RMS andmaximum density matrix error between the iterations [32]The wave function obtained from each calculation has beenanalyzed with the theory of ldquoatoms in moleculesrdquo (AIM)and the atomic property has been calculated using AIMPACprogram [33]

By using EXT94b routine incorporated to the AIMPACsoftware the electron density 120588bcp(119903) Laplacian of electrondensity nabla2120588bcp(119903) and bond ellipticity 120576 have been calculatedfor various applied fields The programs wfn2plots andDENPROP have been used to plot the deformation and theLaplacian of electron densitymapsThe electrostatic potentialof the molecule has been plotted with Gview [34] to visualizethe isosurface of positive and negative ESP regions of themoleculeThe density of states (DOS) at various EFs has beendetermined by usingGuassSumprogram [35] For the variousapplied electric fields (119864) the bias voltage (119881) across themolecule of length 119871 has been calculated from the expression119881 = 119864119871 Further using Ohmrsquos law (119868 = 119881119877) the current (119868)flows through the wire has been calculated for each biasingstep

3 Results and Discussion

31 Structural Aspects The geometric parameters especiallybond lengths are important parameters for adjusting theelectrical properties of molecular wires Also the averagedifference between the adjacent single and double bonds

known as the bond length alternation along the backbone ofa conjugated system plays a vital role for tuning the transportproperties Therefore a detailed study of bond length varia-tion under the EF interaction is instructive for understandingthe relationship between molecular structure and propertyThe optimized geometry of Au and S substituted TTF basedmolecular wire for the zero bias and the maximum appliedEF (020) is illustrated in Table 6 (Optimized geometriesfor various EFs are given in supplementary Figure S1 (seeFigure S1 in Supplementary Material available online athttpdxdoiorg1011552015806181)) This molecular wirehas two aromatic rings with central TTF group and the Auatoms attached at both ends of the molecule through thiolatoms The thiol atom forms an excellent link [36] betweenthe conjugated TTF molecule and the Au atom

For the zero field the CminusC bond distances of twoaromatic rings and the CequivC bonds that link the rings inthe molecule are sim141 and sim122 A respectively When thefield is applied these distances are slightlymodified howeverthe EF dependence of bond length evolution is not identicalfor all the bonds That is the maximum observed variationin CminusC bonds is 0009 whereas CequivC bonds are 0003 AAlso in most cases it is found that the CminusC single bondsbecome shorter and the double and triple bonds becomelonger resulting in higher conjugation which is pertinentto reported results [37 38] The zero field distance of SminusCbonds in the TTF unit is sim183 A as the field increases themaximumvariation observed is 0013 A Similarly the appliedEF alters the bond distances of terminal SminusC bonds whichare found to be unequal on both ends In the left-end (L-end) the distance increases from 1838 to 1842 A while inthe right-end (R-end) the distance decreases from 1837 to1828 A notably the variation in the R-end is slightly greaterthan the L-end and the value is sim0009 A Hence it is foundthat the SminusC bond distances increase in the high potentialside while they decrease in low potential side As the fieldincreases the distance of AuminusS bond in the L-end decreasesfrom 2401 to 2388 A while in the R-end the distanceincreases from 2401 to 2463 A however the variationsin both ends are unequal And for the maximum appliedfield (020VAminus1) the variations at L- and R-ends are 0013and 0038 A respectively This large difference attributesthe applied field lengthening the AuminusS bond through byshrinking the SminusC bond distance in the wire (Table 1) andthese bond distances [SminusC and AuminusS bonds] are very closeto the previously reported values [36 38ndash41] Even thoughalmost all bond distances vary by the application of externalfield specifically the SminusC and AuminusS bonds have uniform andsystematic variation Hence we plot the variation of SminusC andAuminusS bond lengths for different applied EFs with reference tozero fields (Figure 2) The selected values of bond lengths arepresented in Table 1 and the complete values of bond lengthsare listed in supplementary Table S1

32 Charge Density Distribution The selected bond electrondensity values of TTF based molecular wire for zero andvarious levels of applied EF are listed in Table 2 Table 7

Journal of Nanoscience 3

003

002

001

000

minus001

minus002

minus003

Bond

leng

th v

aria

tion

(

S1 S2

S3

S4

S5

S6

C1

C2C3 C4

C5C6

C7

C8

C9

C10

C15C16

C17

C18C19

C20C21

C22

C11 C12C13

C14

Position of bonds

Au1

Au2

000V minus1

004V minus1

008V minus1

012V minus1

016V minus1

020V minus1

AAA

AAA

Au(1

)-S(1

)

Au(2

)-S(2

)

S(1

)-C(

1)

S(4

)-C(

9)

S(3

)-C(

10)

S(3

)-C(

11)

S(4

)-C(

11)

S(5

)-C(

12)

S(6

)-C(

12)

S(5

)-C(

13)

S(6

)-C(

14)

S(2

)-C(

20)

A)

Figure 2 Bond length variations of Au and S substituted TTF basedmolecule for various applied EFs with reference to zero field

Table 1 Bond lengths (A) of terminal bonds of Au and S substitutedTTF based molecule for zero and various applied EFs (VAminus1)

Bonds Applied electric field000 004 008 012 016 020

S(1)ndashC(1) 1838 1839 184 1841 1842 1842S(2)ndashC(20) 1837 1835 1833 1833 1830 1828Au(1)ndashS(1) 2401 2399 2396 2395 2392 2388Au(2)ndashS(2) 2401 2403 2407 2410 2433 2463

Table 2 Electron density 120588bcp(119903) (eAminus3) values of terminal bonds

of Au and S substituted TTF based molecule for zero and variousapplied EFs (VAminus1)



displays the deformation density maps of TTF based molec-ular wire showing the charge accumulation for zero biasand maximum applied field and the differences The relationbetween the topology of electron density and the chemicalconcepts of molecules can be accurately quantified [23] byusing Quantum theory of atoms in molecules (QTAIM) Thecritical point search in the molecule found a (3 minus1) typeof bond critical point (bcp) for all bonds which implies

Table 3 Laplacian of electron density nabla2120588bcp(119903) (eA

minus5) values ofterminal bonds of Au and S substituted TTF basedmolecule for zeroand various applied EFs (VAminus1)


Terminal bondsS(1)ndashC(1) minus4207 minus4186 minus4167 minus4142 minus4123 minus4101S(2)ndashC(20) minus4217 minus4253 minus4297 minus4301 minus4345 minus4387Au(1)ndashS(1) 2950 2971 3014 3024 3218 3409Au(2)ndashS(2) 2954 2947 2925 2925 2925 2925

that the chemical bonds [42 43] exist in the moleculeWe have also found that the interaction between Au andS atoms in AundashS bond of TTF based molecular wire isnot a covalent interaction hence the AundashS bond is a veryweak coordination bond Also the positive Laplacian ofelectron density of AundashS bond (Table 3) shows the existenceof closed shell interaction between the S and Au atoms thisconfirms the noncovalent interaction of AundashS bonds whichis applicable to the reported results [44ndash46]

The zero field electron density [120588bcp(119903)] at the bcp ofall aromatic CminusC bonds ranges from sim1884 to sim1949 eAminus3whereas for the applied field these values are slightly variedand the maximum variation is 0037 eAminus3 Similarly the zerofield electron density120588bcp(119903) of theCminusCbonds connecting thetwo thiophene rings in the TTF unit is sim2092 eAminus3 as thefield increases this value decreases and the observed max-imum electron density variation of the bond is 0019 eAminus3The zero field density of CminusH bond is sim18 eAminus3 this valueis not much altered in the presence of electric field The SminusCbond electron density of thiophene rings for the zero fieldranges from sim0996 to 1084 eAminus3 and for the applied fieldit decreases the maximum variation observed is 0024 eAminus3The CequivC bonds exhibit high electron density for the zerobias (2477 eAminus3) and for the applied field the variation isfound to be very small On comparing the 120588bcp(119903) valuesof CminusC CminusH and SminusC bonds the density of SminusC bondis notably small This indicates that the charges of thesebonds are moving away from the internuclear axis whichconfirms its dominant 120587-bond nature [40] Also this canbe well understood from the Laplacian of electron densityof the molecule compared with the Cremer and Krakarsquoswork [42 43] The AuminusS bond density at zero field is sim

052 eAminus3 whereas for the applied field the density increasesto 0538 eAminus3 in the L-end but in R-end it decreases to0476 eAminus3 Although the electron density of AuminusS bond isvery small the observed variation (0055 eAminus3) is greater thanall other bonds The effect of electric field in the molecule isnot much altered the electron densities of the bond in themolecule Relatively the variations are small for the appliedfield and are found to be very systematic (SupplementaryTable S2) The increase or decrease of applied field in themolecule did not make any significant change in the bondcharge accumulation of the molecule


The Laplacian of the electron density [nabla2120588bcp(119903)] allows tounderstand the charge concentration or depletion at the bcp[42] It plays significant role in the study of the charge density[47 48] In this work the Laplacian values for all bonds in themolecule have been calculated to realize whether the chargesat the bcp of the bonds are concentrated or depleted when themolecules is exposed to external EFs The selected Laplacianof electron density for the various applied EFs is shown inTable 3 Table 8 shows the Laplacian of electron density mapsfor zero and the maximum applied field (020VAminus1) Forthe zero field the predicted Laplacian of electron density forthe aromatic CminusC bonds ranges from minus173 to minus185 eAminus5whereas for the applied field these values become little lessnegative indicating the charges of these bonds are slightlydepleted (Supplementary Figure S2) Similar trend is foundin the CminusC bonds which are connecting the rings in themolecule in which Laplacian for zero field ranges from minus163to minus199 eAminus5 whereas for the applied field the maximumvariation observed is 0314 eAminus5 The zero field Laplacian ofelectron density for the CminusH bonds is sim minus205 eAminus5 thehigh negative value of Laplacian which indicates the chargeconcentration and the applied field slightly alters this chargeconcentration The Laplacian for the terminal SminusC bondsof L-end and R-end is minus4207 and minus4217 eAminus5 respectivelyAs the field increases the Laplacian value in the L-enddecreases to minus4101 eAminus5 and in the R-end it increases tominus4387 eAminus5 For the zero field the Laplacian of AuminusS bondis sim295 eAminus5 when the field increases this value slightlyincreases to 3409 eAminus5 at the L-end but at the R-end itdecreases to 2925 eAminus5 Overall the Laplacian of electrondensity distribution in the Au substituted molecular wire(AuminusSmdashmoleculemdashSminusAu system) reveals that the appliedfield depletes the charges at the bcps of CminusC bonds whereasthis effect is found little more in the terminal bonds (Sup-plementary Figure S3) specifically it is high at the R-endThe complete values of Laplacian of electron density for thevarious applied EFs are shown in supplementary Table S3

33 Energy Density Bond energy density is the measure ofbond strength in a chemical bond The chemical bond is afundamental concept which provides an important basis forrationalizing the structural properties stability and reactivityfor a host of materials In addition to the bond criticalpoint properties the calculated energy density distributionsprovide important information about the local energy densityproperties for the bonded interactions [49] Further theenergy density distribution of TTF based molecule is directlyrelated to Laplacian of electron density [40 42 43] Whenthe Laplacian of electron density is positive the kineticenergy density is dominant which leads to the depletion ofbond charge if it is negative the potential energy densitydominates and the accumulation of charge is expected tohappen [25 42 43] Also the kinetic energy density analysisof TTF identifies patterns within its electronic structurewhich are linked to familiar concepts of chemical bonding[50] The total energy density in the bonding region 119867(r)is expressed as 119867(r) = 119866(r) + 119881(r) where 119881(r) is thepotential energy density and 119866(r) is the local kinetic energy

S2

S3

S4

S5

S6

C1

C2C3 C4

C5C6

C7

C8

C9

C10

C15C16

C17

C18C19

C20C21

C22

C11 C12C13

C14

Au1

Au2

003

004

005

006

007

002

001

000

minus001

minus002

minus003

minus004

minus005

Ener

gy d

ensit

y (H

minus3)

A

Position of bonds

000V minus1

004V minus1

008V minus1

012V minus1

016V minus1

020V minus1

AAA

AAA

Au(1

)-S(1

)

Au(2

)-S(2

)

S(1

)-C(

1)

S(4

)-C(

9)

S(3

)-C(

10)

S(3

)-C(

11)

S(4

)-C(

11)

S(5

)-C(

12)

S(6

)-C(

12)

S(5

)-C(

13)

S(6

)-C(

14)

S(2

)-C(

20)

S1

Figure 3 Energy density variations of Au and S substituted TTFbased molecule for various applied EFs with reference to zero field

density [40] In the case of TTF based molecule 119866(r) ispositive 119881(r) is negative and the total energy density 119867(r)is negative which indicates that 119881(r) dominates for all casesThe calculated zero field energy density 119867(r) for the CminusCbond in the aromatic ring is highly negative which rangesfrom minus1813 to minus1944HAminus3 when the applied EF increasesthese values are slightly decreased within short range (minus1789to minus1936HAminus3)

The zero field energy density 119867(r) for the CminusC bondsin the TTF unit is minus2212HAminus3 when the field increasesthis value decreases to minus2178HAminus3 The energy density ofC(11)ndashC(12) bond connecting the rings varies from minus2268 tominus2226HAminus3 Notably theCequivCbond in themolecule exhibitsthe high energy density (minus3217HAminus3) for the maximumapplied field (020VAminus1) The energy densities 119867(r) forthe CminusH bonds for different fields range from minus1722 tominus1767HAminus3 Notably the energy density distribution in theterminal heavy atom bonds (AundashS and SndashC) is significantlyless (minus0156 and minus062HAminus3) in comparison with the otherbonds in the moleculeThe small values are due to the natureof bonds Further for the applied field the variation betweenboth types of bonds is found to be opposite However thevariations of SminusC and AuminusS bonds are significant and sys-tematic Figure 3 shows the energy density variations of themoleculeThe calculated values of energy density distributionof the terminal bonds of the molecule for zero and various


Table 4 Bond energy density (HAminus3) values of terminal bonds ofAu and S substituted TTF based molecule for the zero and variousapplied EFs (VAminus1)


Terminal bondsS(1)ndashC(1) minus0619 minus0618 minus0617 minus0615 minus0616 minus0671S(2)ndashC(20) minus0621 minus0624 minus0628 minus0629 minus6400 minus0646Au(1)ndashS(1) minus0156 minus0157 minus0159 minus0157 minus0146 minus0161Au(2)ndashS(2) minus0156 minus0155 minus0153 minus0151 minus0144 minus0124

Table 5 Atomic charges (e) of terminal atoms for the zero andvarious applied electric fields (first line CHELPG charges secondline MK charges)

Atom Applied electric field (VAminus1)000 004 008 012 016 020

S(1) minus0333 minus0332 minus0332 minus0331 minus0331 minus0331minus0302 minus0303 minus0302 minus0307 minus0307 minus0293


Au(1) 0175 0177 0177 0179 0181 01830156 0157 0157 0159 0161 0165

Au(2) 0177 0177 0177 0176 0176 01760159 0158 0158 0158 0156 0155

applied EFs are presented in Table 4 and the complete valuesare given in supplementary Table S4

34 Atomic Charges To determine the atomic charges vari-ous methods are available the most frequently used are natu-ral population analysis Mulliken population analysis Chelpgscheme and Merz-kollman (MK) schemes which expressthe electrostatic interactions more precisely The scheme ofpoint charge distribution of molecules plays a major rolein understanding the chemical reactivity and electrostaticpotential [51ndash53] The Chelpg charges are consistent withthe electrostatic Poisson equation Further a number ofstudies have shown that MKmethod provides the best valuesaccording to electrostatic criteria [53 54] Both Chelpg andMK schemes are grid based methods in which the atomiccharges are fitted to reproduce the molecular electrostaticpotential (MEP) at a number of points around the molecule[54 55] Hence in the present work we have calculated thepoint charges by Chelpg and MK schemes

The Chelpg charges of all C-atoms except those whichare linked to S atoms possess negative charge and vary withthe increase of field The linker S(1)-atom possesses negativeChelpg charge which decreases from minus0333 to minus0331 e withincrease of field while the charge of S(2)-atom increases fromminus0333 to minus0348 e As the field increases the charges of Auatom at L-end slightly increase from 0175 to 0183 e but thesame at the R-end almost remains the same (0177 0176 e)For the zero field the MK charge for all C-atoms is foundalmost negative and the H-atoms are positive when thefield increases the charge of the atoms also found increases

For the applied field the MK charges of S-atom at the L-end decrease gradually from minus0302 to minus0293 e while at theR-end this effect is opposite and increases from minus0303 tominus0310 e As the field increases the charge of Au(1) atomincreases from 0156 to 0165 e but the same for Au(2) slightlydecreases from 0159 to 0155 e (Table 5) The differences ofcharge distribution for zero and various applied EFs arepresented in supplementary Table S5

35 Molecular Orbital Analysis Generally for any molecularlevel device the charge transport characteristics are mainlycontrolled by the nature of the molecular orbitalsThe spatialdistribution and the energy level of a molecular orbital (MO)determine its contribution to the conductivity [56 57] Thecharge transfer through a particular MO gradually decreasesas we go away from the Fermi level of the electrode Furtherthe MOs which are fully delocalized contribute more toconduction channel [58ndash61] The frontier molecular orbitalsare the highest occupied molecular orbital (HOMO) andlowest unoccupied molecular orbital (LUMO) and the differ-ence between them is known as HOMO-LUMO gap (HLG)Recently several theoretical studies report the influence ofHOMO-LUMO gaps and the spatial distributions of molecu-lar orbitals on the electronic transport through the moleculardevice [62 63] Further the charge transport properties ofthe molecule [64] are determined by the difference of energybetweenHOMOand LUMOHence it is essential to examinethe variations of HLG and molecular orbital energy levels[64ndash66] for the various applied EFs Table 9 shows the spatialredistribution of molecular orbital of TTF for the zero biasand the maximum applied EF (020VAminus1) The applied EFspartially localize the frontier orbitals (HOMOminus2 HOMOminus1HOMO LUMO LUMO+1 and LUMO+2) of the moleculeswhich are opposite to each other this can be well understoodfrom Table 9

For the applied fields (0ndash020VAminus1) the HLG decreasesfrom 1486 to 0218 eV This variation is also confirmed fromthe spectrum of density of states (DOS) Figures 4(a) and4(b) show the DOS of Au substituted molecule in whichthe HOMO (green lines) and the LUMO (blue lines) andthe HLG are shown Notably the presence of gold atomsin the molecule broadens the DOS peaks Seemingly thesignificant decrease of HLG may facilitate large electronconduction [67 68] through the molecule hence the Ausubstituted TTF based molecule can perform as an efficientmolecular nanowire Figure 5 represents the energy levels ofthe molecule for various applied EFs

36 Electrostatic Potential Molecular electrostatic surfacepotential (ESP) is another piece of information which isrequired to understand the electronic properties ofmolecules[69 70] Areas of the molecule with specific properties suchas electron donation or electron-withdrawing capabilities andtheir stabilities can be easily evaluated from an ESP map[71] this information is extremely useful in understandingmolecular interactions which helps to design molecularelectronic devices [72 73] The isosurface representationof ESP of Au and S substituted TTF based molecule for


HLG = 148 eV

DOS spectrumOccupied orbitals Virtual orbitals

Energy (eV)

DO

S sp

ectr

um (a

u)

3

25

2

15

1

05

0

minus05

minus1minus10 minus8 minus6 minus4 minus2 0

(a)

DO

S sp

ectr

um (a

u)

25

2

15

1

05

0

minus05

minus1


Energy (eV)minus7minus8 minus5minus6 minus4 minus3 minus2 minus1

HLG = 021 eV

(b)

Figure 4 DOS of Au and S substituted TTF based molecule for (a) zero and (b) maximum applied EF (020VAminus1)

Electric field (V minus1)A

minus02 minus01 00 01 02

HOMO minus1

HLG

=148

eV

HLG = 021 eVLUMOHOMO

LUMO +1

Ener

gy (e

V)

64

60

56

52

48

44

40

36

32

28

Figure 5 Energy level diagram of Au and S substituted TTF basedmolecule for the zero and various applied EFs

the various applied EFs is shown in Table 10 The AundashS bondregions exhibit high negative ESP which are the negativecharged regions (red) of themolecule and it explicitly reflectsthe opposing contributions from the nuclei and the electrons

For the zero bias the negative ESP is concentrated aroundthe S-atoms which are present at either ends of the moleculeand also S atoms in the TTF unit The rest of the moleculecarries positive ESP For the increase of positive field from0ndash020VAminus1 the negative ESP at the L-end of the moleculegradually decreases for each biasing step and it disappearswhile the same at the R-end gradually increases and finallyspreads around the right edge of the molecule (Table 10)this shows that when the field increases the charges seem todrift from left to right Similarly the negative ESP regions aremoved from R- to L-end of the molecule when the field isreversedThe ESPmap clearly shows the effect of substitutionand the applied EFs in molecule

37 Molecular Dipole Moment When the molecule is sub-jected to an external EF the delocalization of 120587-electron of

40

30

20

10

0

minus10

minus20

minus30

minus40

000 005 010 015 020

120583x120583y

120583z120583

Dip

ole m

omen

t (de

bye)


Figure 6 Molecular dipole moment of Au and S substituted TTFbased molecule for the zero and various applied EFs

the conjugated organic molecules leads to redistribution ofcharges of the molecular chain and consequently the dipolemoment of the molecule changes [38 74 75] Hence we canroughly estimate the ability of electron transport by simplycomparing the dipole moments of the molecule for variousapplied EFs The variations of molecular dipole moment forthe various applied EFs were analyzed by Kirtman et al [76]and found a linear characterHowever this linearity no longerexists beyond certain applied field and it is unimportantsince no molecular electronic device works under such highvoltages [77] Here we have calculated the dipole momentof the molecule for zero bias as well as various applied EFsThe resultant molecular dipole moment (120583) for zero bias is131 D which increases almost linearly with the increase offield The molecule becomes highly polarized for the higherfield (020VAminus1) and the dipole moment becomes 359DFigure 6 shows the variation of 119909 119910 and 119911 components ofdipole moment (120583

119909

120583119910

and 120583119911

) and the resultant molecular


Table 6 Optimized geometry of Au and S substituted TTF based molecule for the zero and maximum applied EF 020VAminus1

EF (VAminus1) Optimized geometry

000

S(1)S(2)

S(3)

S(4) S(6)

S(5)

H(19)

H(18)

H(10) H(13)

H(21)

H(22)

H(3)

H(6)

H(5)

H(2)C(3)

C(2)

C(1)C(6)

C(7)C(8)

C(9)

C(5)

C(4)

C(10)C(11) C(12)

C(13)

C(14)

C(16)

C(19)

C(20)C(21)

C(22)

C(18)C(17)

C(15)

Au(1) Au(2)

020

S(1)

S(2)

S(3)

S(4) S(6)

S(5)

H(19)

H(18)

H(10) H(13)

H(21)

H(22)

H(3)

H(6)

H(5)

H(2)C(3)

C(2)

C(1)C(6)

C(7)C(8)

C(9)

C(5)

C(4)

C(10)C(11)C(12)

C(13)

C(14)

C(16)C(19)

C(20)C(21)

C(22)

C(18)C(17)

C(15)

Au(1) Au(2)

Table 7 Deformation density maps of Au and S substituted TTFbased molecule for the zero and maximum applied EF 020VAminus1Solid lines represent positive contours dotted lines are negativecontours and dashed lines are zero contours The contours aredrawn at 005 eAminus3 intervals

EF(VAminus1) Deformation density

000

020

dipolemoment (120583) for various applied EFs the large variationof 119909-component [68] may be due to the application of fieldalong 119909-direction

38 119868-119881 Characteristic Curve As a preliminary approachfor calculating the 119868-119881 characteristic of single molecules apurely ab initio approach was developed [78] This methoduses molecular calculations to estimate the 119868-119881 through amolecule Thus formulating a new prescription one canobtain current-voltage characteristics via the use of precisequantum chemistry techniques Here we have evaluated the119868-119881 characteristics of the TTF based molecular wire using

Table 8 Laplacian of electron density maps of Au and S sub-stituted TTF based molecule for the zero and maximum appliedEF 020VAminus1 The contours are drawn in logarithmic scale30times 2119873 eAminus5 where 119873 = 2 4 and 8times 10119899 119899 = minus2 minus1 0 1 2 Solidlines are positive contours and dotted lines are negative contours

EF(VAminus1) Laplacian of electron density

000

020

the Landauer formula [79] The tunneling electric current(119868) has been calculated for various applied electric fields (119864)and the bias voltage (119881) across the molecule of length 119871The linear conductance (119866) and the resistance (119877) of theelectrode-molecule-electrode junctions can be expressed as

119877 = 119866minus1

= (ℎ

21198902)(

1

119879119897

119879119903

119879119898

) =1291KΩ119879119897

119879119903

119879119898

(1)

where 119879119897

and 119879119903

are the charge transport efficiency acrossthe left and right contacts 119879

119898

is the electron transmission


Table 9 Isosurface representation of molecular orbitals of Au and S substituted TTF based molecule for the zero and maximum appliedelectric field (020VAminus1) which are drawn at 005 au surface values

EF (VAminus1) 000 020

LUMO +2

LUMO +1

LUMO

HOMO

HOMO minus1

HOMO minus2

minus6 minus4 minus2 2 4 6

20

40

60

80

minus20

minus40

minus60

minus80

Applied voltage (V)

Curr

ent (120583

A)

Figure 7 119868-119881 Characteristics of Au and S substituted TTF basedmolecule for various applied EFs

through the molecule itself and (ℎ21198902

) = 1291 KΩ is thequantum of resistance [80ndash83] The left and right contactselectron transmission 119879

119897

and 119879119903

can be neglected since thereis no charge injection barrier in the molecule 119879

119898

can beapproximated by the expression

119879119898

= exp (minus120573119871) (2)

where 119871 is the potential barrier width which is equivalentto molecular length and 120573 is the tunneling decay parameterwhich can be determined by

120573 = (1

ℏ) [2119898

lowast

120572120601]12

(3)

where 119898lowast is the effective mass of electron (119898lowast = 0161198980

)1198980

is the free electron mass 120572 is the symmetry parameterof potential profile which is equal to unity for symmetricmolecule [80ndash83] and 120601 is the potential barrier height fortunneling through the HOMO or the LUMO level For aparticular external applied EF 120601 is half of the HLG ofthe molecular wire Hence the resistance of the molecularwire has been calculated using expression (1) Further thebias voltage (119881) has been calculated from the expression119881 = 119864119871 Using these parameters the 119868-119881 characteristicsof the TTF based molecule have been studied Figure 7illustrates the 119868-119881 characteristics of TTF based moleculefor the various applied EFs which reveals that as the biasvoltage increases the current increases gradually showing thenonlinear behavior of the molecule Since the molecule issymmetric the characteristic curve is also almost symmetricfor both directions of the applied EFs

4 Conclusion

The present quantum chemical study on TTF based molec-ular wire describes the bond topological parameters and theelectrical characteristics for zero and various external appliedfields The bond topological analysis shows the variation ofelectron density 120588bcp(119903) and Laplacian of electron densitynabla2

120588bcp(119903) for zero bias and the various applied fields of themolecule Systematic and almost uniform redistribution ofcharge density as well as energy density have been observedfor all bonds of the central TTF unit and terminal bondsof the molecule for various applied EFs When the fieldincreases the hybridization of molecular levels broadens


Table 10 Molecular electrostatic potential of Au and S substituted TTF based molecule for the zero and various applied EFs Blue positivepotential (05 eAminus1) red negative potential (minus004 eAminus1)

EF (VAminus1) Electrostatic potential

000S(6)

S(1) S(2)

S(3)

S(4)

S(5)

H(5)

H(6)

H(2) H(19)

H(18)

H(10) H(13)

H(21)

H(22)

H(3)

C(1)C(2)

C(3)C(4)

C(5)C(6)

C(7)

C(10)C(11) C(12)

C(13)

C(14)

C(16)C(19)

C(20)C(21)

C(22)

C(18)C(17)

C(15)C(9)

C(8)

Au(1)

008

S(1) S(2)

S(3)

S(4) S(6)

S(5)

H(5)

H(6)

H(2) H(19)

H(18)

H(10) H(13)

H(21)

H(22)

H(3)

C(1)C(2)

C(3)C(4)

C(5)C(6)

C(7)

C(10)C(11) C(12)

C(13)

C(14)C(16)

C(19)C(20)C(21)

C(22)

C(18)C(17)

C(15)C(9)

C(8)

Au(1)

012

S(1)

S(2)

S(3)

S(4)

S(5)

H(5)

H(6)

H(2)

H(19)

H(18)

H(10)H(13)

H(21)

H(22)

H(3)

C(1)C(2)

C(3)C(4)

C(5)C(6)

C(7)

C(10)C(11) C(12)

C(13)

C(14)C(16) C(19)C(20)C(21)

C(22)

C(18)C(17)

C(15)C(9)

C(8)

Au(1)

S(6)

020S(1)

S(3) S(5)

S(4) S(6)

H(5)

H(6)

H(2)

H(18)

H(10) H(14)

H(21)

H(22)

H(3)

C(1)

C(2)C(3)

C(4)

C(5)C(6)

C(7)

C(10)C(11) C(12)

C(13)

C(14)C(16) C(17)

C(15)C(9)

C(8)

Au(1)

the DOS and decreases the HLG The large decrease of bandgap from 1486 to 0218 eV at the high field is facilitatedto have high electrical conductivity Also the EF polarizesthe molecule in consequence the dipole moment of themolecule increases from 131 to 359DThe 119868-119881 characteristiccurve is found very symmetric for both directions of appliedEFs it explicitly shows the nonlinear behavior of TTF basedmolecule Further the significant 119868-119881 characteristic detailsof the molecule give an idea to tune the molecule forappropriate biasing voltages for the operation of moleculardevices Over all the terminal groups and the central redoxgroup of TTF unit of the molecular wire are found to be verysensitive to applied EF compared with the molecular regionThe structural confirmation charge density distribution andelectrostatic properties of TTF obtained in the study maysupport design of several kinds of molecular wires based onTTF and its derivatives

Conflict of Interests

The authors declare that there is no conflict of interestsregarding the publication of this paper

References

[1] M Rieth and W Schommers Handbook of Theoretical andComputational Nanotechnology vol 10 American ScientificPublishers 2006

[2] J M Seminario Theoretical and Computational ChemistryElsevier 2007

[3] W Haiss H van Zalinge D Bethell J Ulstrup D J Schiffrinand R J Nichols ldquoThermal gating of the single moleculeconductance of alkanedithiolsrdquoFaradayDiscussions vol 131 pp253ndash264 2006


[4] F Chen J Hihath Z Huang X Li andN J Tao ldquoMeasurementof single-molecule conductancerdquo Annual Review of PhysicalChemistry vol 58 no 1 pp 535ndash564 2007

[5] A Irfan A G Al-Sehemi and A M Asiri ldquoTheoreticalinvestigations of the charge transfer properties in oligothio-phene derivativesrdquo Journal of Theoretical and ComputationalChemistry vol 11 no 3 article 631 2012

[6] L Luo S H Choi and C D Frisbie ldquoProbing hoppingconduction in conjugated molecular wires connected to metalelectrodesrdquo Chemistry of Materials vol 23 no 3 pp 631ndash6452011

[7] X Zeng C Wang M R Bryce et al ldquoFunctionalized 8 nmlong aryleneethynylene molecular wire with alkyne terminirdquoEuropean Journal of Organic Chemistry no 31 pp 5244ndash52492007

[8] A Aviram and M A Ratner ldquoMolecular rectifiersrdquo ChemicalPhysics Letters vol 29 no 2 pp 277ndash283 1974

[9] A Aviram C Joachim and M Pomerantz ldquoEvidence ofswitching and rectification by a single molecule effected with ascanning tunneling microscoperdquo Chemical Physics Letters vol146 pp 490ndash495 1988

[10] J M Tour W A Reinerth L Jones II et al ldquoRecent advances inmolecular scale electronicsrdquoAnnals of the New York Academy ofSciences vol 852 pp 197ndash204 1998

[11] Y W Li J H Yao Z G Zou J W Yang and S R Le ldquoTheoret-ical study of the electron transport through aromatic molecularwires with different levels of conjugationrdquo Computational andTheoretical Chemistry vol 976 pp 135ndash140 2011

[12] S Creager C J Yu C Bamdad et al ldquoElectron transferat electrodes through conjugated ldquomolecular wirerdquo bridgesrdquoJournal of the American Chemical Society vol 121 no 5 pp1059ndash1064 1999

[13] J Ferraris D O Cowan V Walatka Jr and J H PerlsteinldquoElectron transfer in a new highly conducting donor-acceptorcomplexrdquo Journal of the American Chemical Society vol 95 no3 pp 948ndash949 1973

[14] A Amadei M DrsquoAbramo A D Nola A Arcadi G Cerichelliand M Aschi ldquoTheoretical study of intramolecular chargetransfer in 120587-conjugated oligomersrdquo Chemical Physics Lettersvol 434 no 4ndash6 pp 194ndash199 2007

[15] F Wudl and M L Kaplan ldquo221015840 Bi-13-dithiolylidene (tetrathi-afulvalene TTF) and its radical cation derivativesrdquo InorganicSyntheses vol 19 pp 27ndash30 1979

[16] F Wudl D Wobschall and E J Hufnagel ldquoElectrical conduc-tivity by the bis-13-dithiole-bis-13-dithiolium systemrdquo Journalof the American Chemical Society vol 94 no 2 pp 670ndash6721972

[17] M Bendikov F Wudl and D F Perepichka ldquoTetrathiaful-valenes oligoacenenes and their buckminsterfullerene deriva-tives the brick and mortar of organic electronicsrdquo ChemicalReviews vol 104 no 11 pp 4891ndash4945 2004

[18] M Iyoda M Hasegawa and Y Miyake ldquoBi-TTF bis-TTF andrelated TTF oligomersrdquo Chemical Reviews vol 104 no 11 pp5085ndash5113 2004

[19] P Frere and P J Skabara ldquoSalts of extended tetrathiafulvaleneanalogues relationships between molecular structure electro-chemical properties and solid state organisationrdquo ChemicalSociety Reviews vol 34 no 1 pp 69ndash98 2005

[20] X Li J He J Hihath B Xu S M Lindsay and N Tao ldquoCon-ductance of single alkanedithiols conduction mechanism andeffect of molecule-electrode contactsrdquo Journal of the AmericanChemical Society vol 128 no 6 pp 2135ndash2141 2006

[21] W Sheng Z Y Li Z Y Ning Z H Zhang Z Q Yang and HGuo ldquoQuantum transport in alkane molecular wires effects ofbinding modes and anchoring groupsrdquoThe Journal of ChemicalPhysics vol 131 no 24 Article ID 244712 2009

[22] A Gorgues P Hudhomme and M Salle ldquoHighly functional-ized tetrathiafulvalenes riding along the synthetic trail fromelectrophilic alkynesrdquo Chemical Reviews vol 104 no 11 pp5151ndash5184 2004

[23] R F W Bader Atoms in MoleculesmdashA Quantum TheoryClarendon Press Oxford UK 1990

[24] E S Kryachko and E Ludena Density Functional Theory ofAtoms of Many Electron System Kluwer Academic New YorkNY USA 1990

[25] J M Seminario Recent Development and Applications of Mod-ern Density Functional Theory Elesvier New York NY USA1996

[26] D Rai A D Kulkarni S P Gejji and R K Pathak ldquoMethanolclusters (CH

3

OH)119899

n =3ndash6 in external electric fields densityfunctional theory approachrdquo Journal of Chemical Physics vol135 no 2 Article ID 024307 2011

[27] M Das ldquoElectron transfer through non-hydrogen and hydro-gen bonded intermolecular tunnel junctions a computationalstudyrdquo Journal ofTheoretical and Computational Chemistry vol11 p 997 2012

[28] M J Frisch G W Trucks H B Schlegel et al Gaussian IncPittsburgh Pa USA 2003

[29] A D Becke ldquoDensity-functional thermochemistry IIIThe roleof exact exchangerdquoThe Journal of Chemical Physics vol 98 no7 pp 5648ndash5652 1993

[30] P J Hay and W R Wadt ldquoAb initio effective core potentials formolecular calculations Potentials for the transitionmetal atomsSc toHgrdquoThe Journal of Chemical Physics vol 82 no 1 pp 270ndash283 1985

[31] Y Yang M N Weave and K M Merz Jr ldquoAssessment of theldquo6-31+Glowastlowast + LANL2DZrdquo mixed basis set coupled with densityfunctional theory methods and the effective core potentialprediction of heats of formation and ionization potentials forfirst-row-transition-metal complexesrdquo The Journal of PhysicalChemistry A vol 113 no 36 pp 9843ndash9851 2009

[32] H B Schlegel ldquoOptimization of equilibrium geometries andtransition structuresrdquo Journal of Computational Chemistry vol3 no 2 pp 214ndash218 1982

[33] FW Biegler-konig R FW Bader and T H Tang ldquoCalculationof the average properties of atoms in molecules IIrdquo Journal ofComputational Chemistry vol 3 no 3 pp 317ndash328 1982

[34] A Frish E Lecn A B Nielson A J Holder R D Roy Dennig-ton and T A Keith Gaussianlttex cmt=ldquoPlease provide moreinformation for this referencerdquogt Inc Pittsburgh Pa USA2003

[35] N O Boyle GaussSum Revision 21 httpGaussSumsfnet[36] J M Seminario A G Zacarias and J M Tour ldquoMolecular

alligator clips for single molecule electronics Studies of group16 and isonitriles interfaced with Au contactsrdquo Journal of theAmerican Chemical Society vol 121 no 2 pp 411ndash416 1999

[37] Y Zhang Y Ye Y Li X Yin H Liu and J Zhao ldquoAbinitio investigations of quaterthiophene molecular wire underthe interaction of external electric fieldrdquo Journal of MolecularStructure THEOCHEM vol 802 pp 53ndash58 2007

[38] Y Ye M Zhang H Liu X Liu and J Zhao ldquoTheoreticalinvestigation on the oligothienoacenes under the influence ofexternal electric fieldrdquo Journal of Physics andChemistry of Solidsvol 69 no 11 pp 2615ndash2621 2008


[39] A Johanasson and S Stafstrom ldquoInteractions between molecu-lar wires and a gold surfacerdquo Chemical Physics Letters vol 322no 5 pp 301ndash306 2000

[40] P Srinivasan A D Stephen and P Kumaradhas ldquoEffect of goldatom contact in conjugated system of one dimensional octanedithiolate based molecular wire a theoretical charge densitystudyrdquo Journal of Molecular Structure THEOCHEM vol 910no 1ndash3 pp 112ndash121 2009

[41] J Li T Zhu C J Cramer and D G Truhlar ldquoNew class IVcharge model for extracting accurate partial charges from wavefunctionsrdquo Journal of Physical Chemistry A vol 102 no 10 pp1820ndash1831 1998

[42] D Cremer and E Kraka ldquoA description of the chemical bondin terms of local properties of electron density and energyin conceptual approaches in quantum chemistrymdashmodels andapplicationsrdquoCroatia Chemica Acta vol 57 pp 1259ndash1281 1984

[43] D J R Duarte G L Sosa and N M Peruchena ldquoNature ofhalogen bonding A study based on the topological analysisof the Laplacian of the electron charge density and an energydecomposition analysisrdquo Journal of Molecular Modeling vol 19no 5 pp 2035ndash2041 2013

[44] G V Gibbs O Tamada M B Boisen Jr and F C HillldquoLaplacian and bond critical point properties of the electrondensity distributions of sulfide bonds a comparison with oxidebondsrdquoAmericanMineralogist vol 84 no 3 pp 435ndash446 1999

[45] D Rai A D Kulkarni S P Gejji and R K Pathak ldquoIs highelectric field capable of selectively inducing a covalent-like bondbetween polar and non-polar molecular speciesrdquo TheoreticalChemistry Accounts vol 123 pp 501ndash511 2009

[46] R G A Bone and R F W Bader ldquoIdentifying and ana-lyzing intermolecular bonding interactions in van der Waalsmoleculesrdquo Journal of Physical Chemistry vol 100 no 26 pp10892ndash10911 1996

[47] V R Hathwar A K Paul S Natarajan and T N Guru RowldquoCharge density analysis of a pentaborate ion in an ammoniumborate toward the understanding of topological features inborate mineralsrdquo Journal of Physical Chemistry A vol 115 no45 pp 12818ndash12825 2011

[48] R F W Bader and H Essen ldquoThe characterization of atomicinteractionsrdquo The Journal of Chemical Physics vol 80 p 19431984

[49] G V Gibbs R T Downs D F Cox et al ldquoExperimentalbond critical point and local energy density properties deter-mined for Mn-O Fe-O and Co-O bonded interactions fortephroite Mn

2

SiO4

fayalite Fe2

SiO4

and Co2

SiO4

olivine andselected organic metal complexes comparison with propertiescalculated for non-transition and transitionmetal M-O bondedinteractions for silicates and oxidesrdquo The Journal of PhysicalChemistry A vol 112 no 37 pp 8811ndash8823 2008

[50] H Jacobsen ldquoKinetic energy density and covalent bondingmdashacomplementary analysis at the border of bond and no bondrdquoDalton Transactions vol 39 no 23 pp 5426ndash5428 2010

[51] R S Mulliken ldquoElectronic population analysis on LCAO-MOmolecular wave functions Irdquo The Journal of Chemical Physicsvol 23 no 10 pp 1833ndash1840 1955

[52] C Campana BMussard andTKWoo ldquoElectrostatic potentialderived atomic charges for periodic systems using a modifiederror functionalrdquo Journal of ChemicalTheory and Computationvol 5 no 10 pp 2866ndash2878 2009

[53] F Martin and H Zipse ldquoCharge distribution in the watermoleculemdasha comparison ofmethodsrdquo Journal of ComputationalChemistry vol 26 no 1 pp 97ndash105 2005

[54] P A Singh and J Kollman ldquoAn approach to computingelectrostatic charges for moleculesrdquo Journal of ComputationalChemistry vol 5 pp 129ndash145 1984

[55] G S Maciel and E Garcia ldquoCharges derived from electrostaticpotentials exploring dependence on theory and geometry opti-mization levels for dipole momentsrdquo Chemical Physics Lettersvol 409 pp 29ndash33 2005

[56] J M Seminario and L Yan ldquoAb initio analysis of electroncurrents in thioalkanesrdquo International Journal of QuantumChemistry vol 102 no 5 pp 711ndash723 2005

[57] P Wang C N Moorefield S Li S-H Hwang C D Shreinerand G R Newkome ldquoTerpyridineCuII-mediated reversiblenanocomposites of single-wall carbon nanotubes towardsmetallo-nanoscale architecturesrdquo Chemical Communicationsno 10 pp 1091ndash1093 2006

[58] J M Seminario A G Zacarias and P A Derosa ldquoTheoreticalanalysis of complementary molecular memory devicesrdquo TheJournal of Physical ChemistryA vol 105 no 5 pp 791ndash795 2001

[59] J M Seminario R A Araujo and L Yan ldquoNegative differentialresistance in metallic and semiconducting clustersrdquo Journal ofPhysical Chemistry B vol 108 no 22 pp 6915ndash6918 2004

[60] J M Seminario C de la Cruz P A Derosa and L YanldquoNanometer-size conducting and insulatingmolecular devicesrdquoThe Journal of Physical Chemistry B vol 108 no 46 pp 17879ndash17885 2004

[61] L Yan and J M Seminario ldquoElectronic structure and electrontransport characteristics of a cobalt complexrdquo The Journal ofPhysical Chemistry A vol 109 no 30 pp 6628ndash6633 2005

[62] Y Li J Zhao X Yin H Liu and G Yin ldquoConformationalanalysis of diphenylacetylene under the influence of an externalelectric fieldrdquo Physical Chemistry Chemical Physics vol 9 no 10pp 1186ndash1193 2007

[63] C Xia Y Zhang and D Liu ldquoEffect of torsion angle onthe rectifying performance in the donor-bridge-acceptor singlemolecular devicerdquo Journal of Theoretical and ComputationalChemistry vol 11 p 735 2012

[64] W B Davis W A Svec M A Ratner and M R WasielewskildquoMolecular-wire behaviour in p-phenylenevinylene oligomersrdquoNature vol 396 no 6706 pp 60ndash63 1998

[65] Y Zhou K Tan and X Lu ldquoInsights into the solvato-thermo-promoted intramolecular electron transfer in a TTF-120590-TCNQdyad with an extremely low homondashlumo gaprdquo Journal ofTheoretical and Computational Chemistry vol 11 no 3 p 5992012

[66] R J Magyar S Tretiak Y Gao H-LWang and A P Shreve ldquoAjoint theoretical and experimental study of phenylene-acetylenemolecular wiresrdquo Chemical Physics Letters vol 401 no 1ndash3 pp149ndash156 2005

[67] S Hong R Reifenberger W Tian S Datta J I Hendersonand C P Kubiak ldquoMolecular conductance spectroscopy ofconjugated phenyl-based molecules on Au(111) the effectof end groups on molecular conductionrdquo Superlattices andMicrostructures vol 28 no 4 pp 289ndash303 2000

[68] D Farmanzadeh and Z Ashtiani ldquoTheoretical study of aconjugated aromatic molecular wirerdquo Structural Chemistry vol21 no 4 pp 691ndash699 2010

[69] R K Pathak and S R Gadre ldquoMaximal and minimal char-acteristics of molecular electrostatic potentialsrdquo The Journal ofChemical Physics vol 93 no 3 pp 1770ndash1773 1990

[70] P Politzer and D G Thruhlar Chemical Applications of Atomicand Molecular Electrostatic Potential Plenum Press New YorkNY USA 1981


[71] B Hu C Yao and QWang ldquoElectron-withdrawing substitutedbtd-based derivative electronic and optical properties chargetransfer stability studyrdquo Journal of Theoretical and Computa-tional Chemistry vol 10 no 6 pp 829ndash838 2011

[72] J Tomasi B Mennucci M Cammi S Murray and K D SenEds Molecular Electrostatic Potentials Concepts and Applica-tion Elsevier Amsterdam The Netherlands 1996

[73] S R Gadre Computational Chemistry Reviews of CurrentTrends World Scientific Singapore 2000

[74] Y Ye M Zhang and J Zhao ldquoAb initio investigations on threeisomers of polyacetylene under the interaction of the externalelectric fieldrdquo Journal of Molecular Structure THEOCHEM vol822 no 1ndash3 pp 12ndash20 2007

[75] D M Bishop ldquoMolecular vibrational and rotational motion instatic and dynamic electric fieldsrdquo Reviews of Modern Physicsvol 62 no 2 pp 343ndash374 1990

[76] B Kirtman B Champagne and D M J Bishop ldquoElectricfield simulation of substituents in donor-acceptor polyenesa comparison with ab initio predictions for dipole momentspolarizabilities and hyperpolarizabilitiesrdquo Journal of the Amer-ican Chemical Society vol 122 no 33 pp 8007ndash8012 2002

[77] NCGreenhamRH FriendH Enhrenreich and F SpacepenSolid State Physics Academic Press SanDiego Calif USA 1995

[78] J M Seminario A G Zacarias and J M Tour ldquoMolecularcurrentmdashvoltage characteristicsrdquoThe Journal of Physical Chem-istry A vol 103 no 39 pp 7883ndash7887 1999

[79] R Landauer ldquoCan a length of perfect conductor have a resis-tancerdquo Physics Letters A vol 85 no 2 pp 91ndash93 1981

[80] J G Kushmerick J Naciri J C Yang and R ShashidharldquoConductance scaling of molecular wires in parallelrdquo NanoLetters vol 3 no 7 pp 897ndash900 2003


[82] M D Ganji and A Mir-Hashemi ldquoAb initio investigation ofthe I-V characteristics of the butadiene nano-molecular wiresa light-driven molecular switchrdquo Physics Letters Section AGeneral Atomic and Solid State Physics vol 372 no 17 pp3058ndash3063 2008

[83] K Selvaraju M Jothi and P Kumaradhas ldquoA charge den-sity analysis on quarter thiophene molecular nanowire underapplied electric field a theoretical studyrdquo Journal of Computa-tional and Theoretical Nanoscience vol 10 no 2 pp 357ndash3672013

Submit your manuscripts athttpwwwhindawicom

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materials


Journal ofNanomaterials


Au AuS

SS

S

S S

219nm

Figure 1 Au and S substituted tetrathiafulvalene (TTF) basedmolecule

theory of atoms inmolecules (AIM) [23 24]makes it possibleto determine the above properties for zero bias and variousapplied EFs

2 Computational Details

Understanding the effect of applied electric field on thestructural and electronic properties of the Au and thiol sub-stituted TTF basedmolecule has been analyzed by optimizingit for the zero and applied fields for both directions [fivebiasing steps plusmn004 plusmn008 plusmn012 plusmn016 and plusmn020VAminus1] Allcalculations in this study have been carried out using densityfunctional theory (DFT) [23ndash27] Gaussian03 program [28]is used throughout all computations Here we have usedLANL2DZ basis set [29] for whole DFT calculation withB3LYP hybrid function to obtain effective core potential andthe detailed description of the effect of heavy metal atomsin the molecule [29ndash31] All geometric optimizations havebeen performed via Berny algorithm in redundant internalcoordinates The self-consistency of noninteractive wavefunction has been performed with a requested convergenceon the density matrix of 10minus8 and 10minus6 for the RMS andmaximum density matrix error between the iterations [32]The wave function obtained from each calculation has beenanalyzed with the theory of ldquoatoms in moleculesrdquo (AIM)and the atomic property has been calculated using AIMPACprogram [33]

By using EXT94b routine incorporated to the AIMPACsoftware the electron density 120588bcp(119903) Laplacian of electrondensity nabla2120588bcp(119903) and bond ellipticity 120576 have been calculatedfor various applied fields The programs wfn2plots andDENPROP have been used to plot the deformation and theLaplacian of electron densitymapsThe electrostatic potentialof the molecule has been plotted with Gview [34] to visualizethe isosurface of positive and negative ESP regions of themoleculeThe density of states (DOS) at various EFs has beendetermined by usingGuassSumprogram [35] For the variousapplied electric fields (119864) the bias voltage (119881) across themolecule of length 119871 has been calculated from the expression119881 = 119864119871 Further using Ohmrsquos law (119868 = 119881119877) the current (119868)flows through the wire has been calculated for each biasingstep

3 Results and Discussion

31 Structural Aspects The geometric parameters especiallybond lengths are important parameters for adjusting theelectrical properties of molecular wires Also the averagedifference between the adjacent single and double bonds

known as the bond length alternation along the backbone ofa conjugated system plays a vital role for tuning the transportproperties Therefore a detailed study of bond length varia-tion under the EF interaction is instructive for understandingthe relationship between molecular structure and propertyThe optimized geometry of Au and S substituted TTF basedmolecular wire for the zero bias and the maximum appliedEF (020) is illustrated in Table 6 (Optimized geometriesfor various EFs are given in supplementary Figure S1 (seeFigure S1 in Supplementary Material available online athttpdxdoiorg1011552015806181)) This molecular wirehas two aromatic rings with central TTF group and the Auatoms attached at both ends of the molecule through thiolatoms The thiol atom forms an excellent link [36] betweenthe conjugated TTF molecule and the Au atom

For the zero field the CminusC bond distances of twoaromatic rings and the CequivC bonds that link the rings inthe molecule are sim141 and sim122 A respectively When thefield is applied these distances are slightlymodified howeverthe EF dependence of bond length evolution is not identicalfor all the bonds That is the maximum observed variationin CminusC bonds is 0009 whereas CequivC bonds are 0003 AAlso in most cases it is found that the CminusC single bondsbecome shorter and the double and triple bonds becomelonger resulting in higher conjugation which is pertinentto reported results [37 38] The zero field distance of SminusCbonds in the TTF unit is sim183 A as the field increases themaximumvariation observed is 0013 A Similarly the appliedEF alters the bond distances of terminal SminusC bonds whichare found to be unequal on both ends In the left-end (L-end) the distance increases from 1838 to 1842 A while inthe right-end (R-end) the distance decreases from 1837 to1828 A notably the variation in the R-end is slightly greaterthan the L-end and the value is sim0009 A Hence it is foundthat the SminusC bond distances increase in the high potentialside while they decrease in low potential side As the fieldincreases the distance of AuminusS bond in the L-end decreasesfrom 2401 to 2388 A while in the R-end the distanceincreases from 2401 to 2463 A however the variationsin both ends are unequal And for the maximum appliedfield (020VAminus1) the variations at L- and R-ends are 0013and 0038 A respectively This large difference attributesthe applied field lengthening the AuminusS bond through byshrinking the SminusC bond distance in the wire (Table 1) andthese bond distances [SminusC and AuminusS bonds] are very closeto the previously reported values [36 38ndash41] Even thoughalmost all bond distances vary by the application of externalfield specifically the SminusC and AuminusS bonds have uniform andsystematic variation Hence we plot the variation of SminusC andAuminusS bond lengths for different applied EFs with reference tozero fields (Figure 2) The selected values of bond lengths arepresented in Table 1 and the complete values of bond lengthsare listed in supplementary Table S1

32 Charge Density Distribution The selected bond electrondensity values of TTF based molecular wire for zero andvarious levels of applied EF are listed in Table 2 Table 7


003

002

001

000

minus001

minus002

minus003

Bond

leng

th v

aria

tion

(

S1 S2

S3

S4

S5

S6

C1

C2C3 C4

C5C6

C7

C8

C9

C10

C15C16

C17

C18C19

C20C21

C22

C11 C12C13

C14

Position of bonds

Au1

Au2

000V minus1

004V minus1

008V minus1

012V minus1

016V minus1

020V minus1

AAA

AAA

Au(1

)-S(1

)

Au(2

)-S(2

)

S(1

)-C(

1)

S(4

)-C(

9)

S(3

)-C(

10)

S(3

)-C(

11)

S(4

)-C(

11)

S(5

)-C(

12)

S(6

)-C(

12)

S(5

)-C(

13)

S(6

)-C(

14)

S(2

)-C(

20)

A)




















S2

S3

S4

S5

S6

C1

C2C3 C4

C5C6

C7

C8

C9

C10

C15C16

C17

C18C19

C20C21

C22

C11 C12C13

C14

Au1

Au2

003

004

005

006

007

002

001

000

minus001

minus002

minus003

minus004

minus005

Ener

gy d

ensit

y (H

minus3)

A

Position of bonds

000V minus1

004V minus1

008V minus1

012V minus1

016V minus1

020V minus1

AAA

AAA

Au(1

)-S(1

)

Au(2

)-S(2

)

S(1

)-C(

1)

S(4

)-C(

9)

S(3

)-C(

10)

S(3

)-C(

11)

S(4

)-C(

11)

S(5

)-C(

12)

S(6

)-C(

12)

S(5

)-C(

13)

S(6

)-C(

14)

S(2

)-C(

20)

S1












Au(1) 0175 0177 0177 0179 0181 01830156 0157 0157 0159 0161 0165

Au(2) 0177 0177 0177 0176 0176 01760159 0158 0158 0158 0156 0155









HLG = 148 eV


Energy (eV)

DO

S sp

ectr

um (a

u)

3

25

2

15

1

05

0

minus05


(a)

DO

S sp

ectr

um (a

u)

25

2

15

1

05

0

minus05

minus1



HLG = 021 eV

(b)




HOMO minus1

HLG

=148

eV


LUMO +1

Ener

gy (e

V)

64

60

56

52

48

44

40

36

32

28





40

30

20

10

0

minus10

minus20

minus30

minus40

000 005 010 015 020

120583x120583y

120583z120583

Dip

ole m

omen

t (de

bye)




119909

120583119910

and 120583119911





000

S(1)S(2)

S(3)

S(4) S(6)

S(5)

H(19)

H(18)

H(10) H(13)

H(21)

H(22)

H(3)

H(6)

H(5)

H(2)C(3)

C(2)

C(1)C(6)

C(7)C(8)

C(9)

C(5)

C(4)

C(10)C(11) C(12)

C(13)

C(14)

C(16)

C(19)

C(20)C(21)

C(22)

C(18)C(17)

C(15)

Au(1) Au(2)

020

S(1)

S(2)

S(3)

S(4) S(6)

S(5)

H(19)

H(18)

H(10) H(13)

H(21)

H(22)

H(3)

H(6)

H(5)

H(2)C(3)

C(2)

C(1)C(6)

C(7)C(8)

C(9)

C(5)

C(4)

C(10)C(11)C(12)

C(13)

C(14)

C(16)C(19)

C(20)C(21)

C(22)

C(18)C(17)

C(15)

Au(1) Au(2)



000

020





000

020


119877 = 119866minus1

= (ℎ

21198902)(

1

119879119897

119879119903

119879119898

) =1291KΩ119879119897

119879119903

119879119898

(1)

where 119879119897

and 119879119903


119898





LUMO +2

LUMO +1

LUMO

HOMO

HOMO minus1

HOMO minus2


20

40

60

80

minus20

minus40

minus60

minus80

Applied voltage (V)

Curr

ent (120583

A)




119897

and 119879119903


119898


119879119898

= exp (minus120573119871) (2)


120573 = (1

ℏ) [2119898

lowast

120572120601]12

(3)


)1198980


4 Conclusion






000S(6)

S(1) S(2)

S(3)

S(4)

S(5)

H(5)

H(6)

H(2) H(19)

H(18)

H(10) H(13)

H(21)

H(22)

H(3)

C(1)C(2)

C(3)C(4)

C(5)C(6)

C(7)

C(10)C(11) C(12)

C(13)

C(14)

C(16)C(19)

C(20)C(21)

C(22)

C(18)C(17)

C(15)C(9)

C(8)

Au(1)

008

S(1) S(2)

S(3)

S(4) S(6)

S(5)

H(5)

H(6)

H(2) H(19)

H(18)

H(10) H(13)

H(21)

H(22)

H(3)

C(1)C(2)

C(3)C(4)

C(5)C(6)

C(7)

C(10)C(11) C(12)

C(13)

C(14)C(16)

C(19)C(20)C(21)

C(22)

C(18)C(17)

C(15)C(9)

C(8)

Au(1)

012

S(1)

S(2)

S(3)

S(4)

S(5)

H(5)

H(6)

H(2)

H(19)

H(18)

H(10)H(13)

H(21)

H(22)

H(3)

C(1)C(2)

C(3)C(4)

C(5)C(6)

C(7)

C(10)C(11) C(12)

C(13)

C(14)C(16) C(19)C(20)C(21)

C(22)

C(18)C(17)

C(15)C(9)

C(8)

Au(1)

S(6)

020S(1)

S(3) S(5)

S(4) S(6)

H(5)

H(6)

H(2)

H(18)

H(10) H(14)

H(21)

H(22)

H(3)

C(1)

C(2)C(3)

C(4)

C(5)C(6)

C(7)

C(10)C(11) C(12)

C(13)

C(14)C(16) C(17)

C(15)C(9)

C(8)

Au(1)




References




























3

OH)119899


























2

SiO4

fayalite Fe2

SiO4

and Co2

SiO4












































CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials




003

002

001

000

minus001

minus002

minus003

Bond

leng

th v

aria

tion

(

S1 S2

S3

S4

S5

S6

C1

C2C3 C4

C5C6

C7

C8

C9

C10

C15C16

C17

C18C19

C20C21

C22

C11 C12C13

C14

Position of bonds

Au1

Au2

000V minus1

004V minus1

008V minus1

012V minus1

016V minus1

020V minus1

AAA

AAA

Au(1

)-S(1

)

Au(2

)-S(2

)

S(1

)-C(

1)

S(4

)-C(

9)

S(3

)-C(

10)

S(3

)-C(

11)

S(4

)-C(

11)

S(5

)-C(

12)

S(6

)-C(

12)

S(5

)-C(

13)

S(6

)-C(

14)

S(2

)-C(

20)

A)




















S2

S3

S4

S5

S6

C1

C2C3 C4

C5C6

C7

C8

C9

C10

C15C16

C17

C18C19

C20C21

C22

C11 C12C13

C14

Au1

Au2

003

004

005

006

007

002

001

000

minus001

minus002

minus003

minus004

minus005

Ener

gy d

ensit

y (H

minus3)

A

Position of bonds

000V minus1

004V minus1

008V minus1

012V minus1

016V minus1

020V minus1

AAA

AAA

Au(1

)-S(1

)

Au(2

)-S(2

)

S(1

)-C(

1)

S(4

)-C(

9)

S(3

)-C(

10)

S(3

)-C(

11)

S(4

)-C(

11)

S(5

)-C(

12)

S(6

)-C(

12)

S(5

)-C(

13)

S(6

)-C(

14)

S(2

)-C(

20)

S1












Au(1) 0175 0177 0177 0179 0181 01830156 0157 0157 0159 0161 0165

Au(2) 0177 0177 0177 0176 0176 01760159 0158 0158 0158 0156 0155









HLG = 148 eV


Energy (eV)

DO

S sp

ectr

um (a

u)

3

25

2

15

1

05

0

minus05


(a)

DO

S sp

ectr

um (a

u)

25

2

15

1

05

0

minus05

minus1



HLG = 021 eV

(b)




HOMO minus1

HLG

=148

eV


LUMO +1

Ener

gy (e

V)

64

60

56

52

48

44

40

36

32

28





40

30

20

10

0

minus10

minus20

minus30

minus40

000 005 010 015 020

120583x120583y

120583z120583

Dip

ole m

omen

t (de

bye)




119909

120583119910

and 120583119911





000

S(1)S(2)

S(3)

S(4) S(6)

S(5)

H(19)

H(18)

H(10) H(13)

H(21)

H(22)

H(3)

H(6)

H(5)

H(2)C(3)

C(2)

C(1)C(6)

C(7)C(8)

C(9)

C(5)

C(4)

C(10)C(11) C(12)

C(13)

C(14)

C(16)

C(19)

C(20)C(21)

C(22)

C(18)C(17)

C(15)

Au(1) Au(2)

020

S(1)

S(2)

S(3)

S(4) S(6)

S(5)

H(19)

H(18)

H(10) H(13)

H(21)

H(22)

H(3)

H(6)

H(5)

H(2)C(3)

C(2)

C(1)C(6)

C(7)C(8)

C(9)

C(5)

C(4)

C(10)C(11)C(12)

C(13)

C(14)

C(16)C(19)

C(20)C(21)

C(22)

C(18)C(17)

C(15)

Au(1) Au(2)



000

020





000

020


119877 = 119866minus1

= (ℎ

21198902)(

1

119879119897

119879119903

119879119898

) =1291KΩ119879119897

119879119903

119879119898

(1)

where 119879119897

and 119879119903


119898





LUMO +2

LUMO +1

LUMO

HOMO

HOMO minus1

HOMO minus2


20

40

60

80

minus20

minus40

minus60

minus80

Applied voltage (V)

Curr

ent (120583

A)




119897

and 119879119903


119898


119879119898

= exp (minus120573119871) (2)


120573 = (1

ℏ) [2119898

lowast

120572120601]12

(3)


)1198980


4 Conclusion






000S(6)

S(1) S(2)

S(3)

S(4)

S(5)

H(5)

H(6)

H(2) H(19)

H(18)

H(10) H(13)

H(21)

H(22)

H(3)

C(1)C(2)

C(3)C(4)

C(5)C(6)

C(7)

C(10)C(11) C(12)

C(13)

C(14)

C(16)C(19)

C(20)C(21)

C(22)

C(18)C(17)

C(15)C(9)

C(8)

Au(1)

008

S(1) S(2)

S(3)

S(4) S(6)

S(5)

H(5)

H(6)

H(2) H(19)

H(18)

H(10) H(13)

H(21)

H(22)

H(3)

C(1)C(2)

C(3)C(4)

C(5)C(6)

C(7)

C(10)C(11) C(12)

C(13)

C(14)C(16)

C(19)C(20)C(21)

C(22)

C(18)C(17)

C(15)C(9)

C(8)

Au(1)

012

S(1)

S(2)

S(3)

S(4)

S(5)

H(5)

H(6)

H(2)

H(19)

H(18)

H(10)H(13)

H(21)

H(22)

H(3)

C(1)C(2)

C(3)C(4)

C(5)C(6)

C(7)

C(10)C(11) C(12)

C(13)

C(14)C(16) C(19)C(20)C(21)

C(22)

C(18)C(17)

C(15)C(9)

C(8)

Au(1)

S(6)

020S(1)

S(3) S(5)

S(4) S(6)

H(5)

H(6)

H(2)

H(18)

H(10) H(14)

H(21)

H(22)

H(3)

C(1)

C(2)C(3)

C(4)

C(5)C(6)

C(7)

C(10)C(11) C(12)

C(13)

C(14)C(16) C(17)

C(15)C(9)

C(8)

Au(1)




References




























3

OH)119899


























2

SiO4

fayalite Fe2

SiO4

and Co2

SiO4












































CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials






S2

S3

S4

S5

S6

C1

C2C3 C4

C5C6

C7

C8

C9

C10

C15C16

C17

C18C19

C20C21

C22

C11 C12C13

C14

Au1

Au2

003

004

005

006

007

002

001

000

minus001

minus002

minus003

minus004

minus005

Ener

gy d

ensit

y (H

minus3)

A

Position of bonds

000V minus1

004V minus1

008V minus1

012V minus1

016V minus1

020V minus1

AAA

AAA

Au(1

)-S(1

)

Au(2

)-S(2

)

S(1

)-C(

1)

S(4

)-C(

9)

S(3

)-C(

10)

S(3

)-C(

11)

S(4

)-C(

11)

S(5

)-C(

12)

S(6

)-C(

12)

S(5

)-C(

13)

S(6

)-C(

14)

S(2

)-C(

20)

S1












Au(1) 0175 0177 0177 0179 0181 01830156 0157 0157 0159 0161 0165

Au(2) 0177 0177 0177 0176 0176 01760159 0158 0158 0158 0156 0155









HLG = 148 eV


Energy (eV)

DO

S sp

ectr

um (a

u)

3

25

2

15

1

05

0

minus05


(a)

DO

S sp

ectr

um (a

u)

25

2

15

1

05

0

minus05

minus1



HLG = 021 eV

(b)




HOMO minus1

HLG

=148

eV


LUMO +1

Ener

gy (e

V)

64

60

56

52

48

44

40

36

32

28





40

30

20

10

0

minus10

minus20

minus30

minus40

000 005 010 015 020

120583x120583y

120583z120583

Dip

ole m

omen

t (de

bye)




119909

120583119910

and 120583119911





000

S(1)S(2)

S(3)

S(4) S(6)

S(5)

H(19)

H(18)

H(10) H(13)

H(21)

H(22)

H(3)

H(6)

H(5)

H(2)C(3)

C(2)

C(1)C(6)

C(7)C(8)

C(9)

C(5)

C(4)

C(10)C(11) C(12)

C(13)

C(14)

C(16)

C(19)

C(20)C(21)

C(22)

C(18)C(17)

C(15)

Au(1) Au(2)

020

S(1)

S(2)

S(3)

S(4) S(6)

S(5)

H(19)

H(18)

H(10) H(13)

H(21)

H(22)

H(3)

H(6)

H(5)

H(2)C(3)

C(2)

C(1)C(6)

C(7)C(8)

C(9)

C(5)

C(4)

C(10)C(11)C(12)

C(13)

C(14)

C(16)C(19)

C(20)C(21)

C(22)

C(18)C(17)

C(15)

Au(1) Au(2)



000

020





000

020


119877 = 119866minus1

= (ℎ

21198902)(

1

119879119897

119879119903

119879119898

) =1291KΩ119879119897

119879119903

119879119898

(1)

where 119879119897

and 119879119903


119898





LUMO +2

LUMO +1

LUMO

HOMO

HOMO minus1

HOMO minus2


20

40

60

80

minus20

minus40

minus60

minus80

Applied voltage (V)

Curr

ent (120583

A)




119897

and 119879119903


119898


119879119898

= exp (minus120573119871) (2)


120573 = (1

ℏ) [2119898

lowast

120572120601]12

(3)


)1198980


4 Conclusion






000S(6)

S(1) S(2)

S(3)

S(4)

S(5)

H(5)

H(6)

H(2) H(19)

H(18)

H(10) H(13)

H(21)

H(22)

H(3)

C(1)C(2)

C(3)C(4)

C(5)C(6)

C(7)

C(10)C(11) C(12)

C(13)

C(14)

C(16)C(19)

C(20)C(21)

C(22)

C(18)C(17)

C(15)C(9)

C(8)

Au(1)

008

S(1) S(2)

S(3)

S(4) S(6)

S(5)

H(5)

H(6)

H(2) H(19)

H(18)

H(10) H(13)

H(21)

H(22)

H(3)

C(1)C(2)

C(3)C(4)

C(5)C(6)

C(7)

C(10)C(11) C(12)

C(13)

C(14)C(16)

C(19)C(20)C(21)

C(22)

C(18)C(17)

C(15)C(9)

C(8)

Au(1)

012

S(1)

S(2)

S(3)

S(4)

S(5)

H(5)

H(6)

H(2)

H(19)

H(18)

H(10)H(13)

H(21)

H(22)

H(3)

C(1)C(2)

C(3)C(4)

C(5)C(6)

C(7)

C(10)C(11) C(12)

C(13)

C(14)C(16) C(19)C(20)C(21)

C(22)

C(18)C(17)

C(15)C(9)

C(8)

Au(1)

S(6)

020S(1)

S(3) S(5)

S(4) S(6)

H(5)

H(6)

H(2)

H(18)

H(10) H(14)

H(21)

H(22)

H(3)

C(1)

C(2)C(3)

C(4)

C(5)C(6)

C(7)

C(10)C(11) C(12)

C(13)

C(14)C(16) C(17)

C(15)C(9)

C(8)

Au(1)




References




























3

OH)119899


























2

SiO4

fayalite Fe2

SiO4

and Co2

SiO4












































CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials











Au(1) 0175 0177 0177 0179 0181 01830156 0157 0157 0159 0161 0165

Au(2) 0177 0177 0177 0176 0176 01760159 0158 0158 0158 0156 0155









HLG = 148 eV


Energy (eV)

DO

S sp

ectr

um (a

u)

3

25

2

15

1

05

0

minus05


(a)

DO

S sp

ectr

um (a

u)

25

2

15

1

05

0

minus05

minus1



HLG = 021 eV

(b)




HOMO minus1

HLG

=148

eV


LUMO +1

Ener

gy (e

V)

64

60

56

52

48

44

40

36

32

28





40

30

20

10

0

minus10

minus20

minus30

minus40

000 005 010 015 020

120583x120583y

120583z120583

Dip

ole m

omen

t (de

bye)




119909

120583119910

and 120583119911





000

S(1)S(2)

S(3)

S(4) S(6)

S(5)

H(19)

H(18)

H(10) H(13)

H(21)

H(22)

H(3)

H(6)

H(5)

H(2)C(3)

C(2)

C(1)C(6)

C(7)C(8)

C(9)

C(5)

C(4)

C(10)C(11) C(12)

C(13)

C(14)

C(16)

C(19)

C(20)C(21)

C(22)

C(18)C(17)

C(15)

Au(1) Au(2)

020

S(1)

S(2)

S(3)

S(4) S(6)

S(5)

H(19)

H(18)

H(10) H(13)

H(21)

H(22)

H(3)

H(6)

H(5)

H(2)C(3)

C(2)

C(1)C(6)

C(7)C(8)

C(9)

C(5)

C(4)

C(10)C(11)C(12)

C(13)

C(14)

C(16)C(19)

C(20)C(21)

C(22)

C(18)C(17)

C(15)

Au(1) Au(2)



000

020





000

020


119877 = 119866minus1

= (ℎ

21198902)(

1

119879119897

119879119903

119879119898

) =1291KΩ119879119897

119879119903

119879119898

(1)

where 119879119897

and 119879119903


119898





LUMO +2

LUMO +1

LUMO

HOMO

HOMO minus1

HOMO minus2


20

40

60

80

minus20

minus40

minus60

minus80

Applied voltage (V)

Curr

ent (120583

A)




119897

and 119879119903


119898


119879119898

= exp (minus120573119871) (2)


120573 = (1

ℏ) [2119898

lowast

120572120601]12

(3)


)1198980


4 Conclusion






000S(6)

S(1) S(2)

S(3)

S(4)

S(5)

H(5)

H(6)

H(2) H(19)

H(18)

H(10) H(13)

H(21)

H(22)

H(3)

C(1)C(2)

C(3)C(4)

C(5)C(6)

C(7)

C(10)C(11) C(12)

C(13)

C(14)

C(16)C(19)

C(20)C(21)

C(22)

C(18)C(17)

C(15)C(9)

C(8)

Au(1)

008

S(1) S(2)

S(3)

S(4) S(6)

S(5)

H(5)

H(6)

H(2) H(19)

H(18)

H(10) H(13)

H(21)

H(22)

H(3)

C(1)C(2)

C(3)C(4)

C(5)C(6)

C(7)

C(10)C(11) C(12)

C(13)

C(14)C(16)

C(19)C(20)C(21)

C(22)

C(18)C(17)

C(15)C(9)

C(8)

Au(1)

012

S(1)

S(2)

S(3)

S(4)

S(5)

H(5)

H(6)

H(2)

H(19)

H(18)

H(10)H(13)

H(21)

H(22)

H(3)

C(1)C(2)

C(3)C(4)

C(5)C(6)

C(7)

C(10)C(11) C(12)

C(13)

C(14)C(16) C(19)C(20)C(21)

C(22)

C(18)C(17)

C(15)C(9)

C(8)

Au(1)

S(6)

020S(1)

S(3) S(5)

S(4) S(6)

H(5)

H(6)

H(2)

H(18)

H(10) H(14)

H(21)

H(22)

H(3)

C(1)

C(2)C(3)

C(4)

C(5)C(6)

C(7)

C(10)C(11) C(12)

C(13)

C(14)C(16) C(17)

C(15)C(9)

C(8)

Au(1)




References




























3

OH)119899


























2

SiO4

fayalite Fe2

SiO4

and Co2

SiO4












































CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials




HLG = 148 eV


Energy (eV)

DO

S sp

ectr

um (a

u)

3

25

2

15

1

05

0

minus05


(a)

DO

S sp

ectr

um (a

u)

25

2

15

1

05

0

minus05

minus1



HLG = 021 eV

(b)




HOMO minus1

HLG

=148

eV


LUMO +1

Ener

gy (e

V)

64

60

56

52

48

44

40

36

32

28





40

30

20

10

0

minus10

minus20

minus30

minus40

000 005 010 015 020

120583x120583y

120583z120583

Dip

ole m

omen

t (de

bye)




119909

120583119910

and 120583119911





000

S(1)S(2)

S(3)

S(4) S(6)

S(5)

H(19)

H(18)

H(10) H(13)

H(21)

H(22)

H(3)

H(6)

H(5)

H(2)C(3)

C(2)

C(1)C(6)

C(7)C(8)

C(9)

C(5)

C(4)

C(10)C(11) C(12)

C(13)

C(14)

C(16)

C(19)

C(20)C(21)

C(22)

C(18)C(17)

C(15)

Au(1) Au(2)

020

S(1)

S(2)

S(3)

S(4) S(6)

S(5)

H(19)

H(18)

H(10) H(13)

H(21)

H(22)

H(3)

H(6)

H(5)

H(2)C(3)

C(2)

C(1)C(6)

C(7)C(8)

C(9)

C(5)

C(4)

C(10)C(11)C(12)

C(13)

C(14)

C(16)C(19)

C(20)C(21)

C(22)

C(18)C(17)

C(15)

Au(1) Au(2)



000

020





000

020


119877 = 119866minus1

= (ℎ

21198902)(

1

119879119897

119879119903

119879119898

) =1291KΩ119879119897

119879119903

119879119898

(1)

where 119879119897

and 119879119903


119898





LUMO +2

LUMO +1

LUMO

HOMO

HOMO minus1

HOMO minus2


20

40

60

80

minus20

minus40

minus60

minus80

Applied voltage (V)

Curr

ent (120583

A)




119897

and 119879119903


119898


119879119898

= exp (minus120573119871) (2)


120573 = (1

ℏ) [2119898

lowast

120572120601]12

(3)


)1198980


4 Conclusion






000S(6)

S(1) S(2)

S(3)

S(4)

S(5)

H(5)

H(6)

H(2) H(19)

H(18)

H(10) H(13)

H(21)

H(22)

H(3)

C(1)C(2)

C(3)C(4)

C(5)C(6)

C(7)

C(10)C(11) C(12)

C(13)

C(14)

C(16)C(19)

C(20)C(21)

C(22)

C(18)C(17)

C(15)C(9)

C(8)

Au(1)

008

S(1) S(2)

S(3)

S(4) S(6)

S(5)

H(5)

H(6)

H(2) H(19)

H(18)

H(10) H(13)

H(21)

H(22)

H(3)

C(1)C(2)

C(3)C(4)

C(5)C(6)

C(7)

C(10)C(11) C(12)

C(13)

C(14)C(16)

C(19)C(20)C(21)

C(22)

C(18)C(17)

C(15)C(9)

C(8)

Au(1)

012

S(1)

S(2)

S(3)

S(4)

S(5)

H(5)

H(6)

H(2)

H(19)

H(18)

H(10)H(13)

H(21)

H(22)

H(3)

C(1)C(2)

C(3)C(4)

C(5)C(6)

C(7)

C(10)C(11) C(12)

C(13)

C(14)C(16) C(19)C(20)C(21)

C(22)

C(18)C(17)

C(15)C(9)

C(8)

Au(1)

S(6)

020S(1)

S(3) S(5)

S(4) S(6)

H(5)

H(6)

H(2)

H(18)

H(10) H(14)

H(21)

H(22)

H(3)

C(1)

C(2)C(3)

C(4)

C(5)C(6)

C(7)

C(10)C(11) C(12)

C(13)

C(14)C(16) C(17)

C(15)C(9)

C(8)

Au(1)




References




























3

OH)119899


























2

SiO4

fayalite Fe2

SiO4

and Co2

SiO4












































CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials






000

S(1)S(2)

S(3)

S(4) S(6)

S(5)

H(19)

H(18)

H(10) H(13)

H(21)

H(22)

H(3)

H(6)

H(5)

H(2)C(3)

C(2)

C(1)C(6)

C(7)C(8)

C(9)

C(5)

C(4)

C(10)C(11) C(12)

C(13)

C(14)

C(16)

C(19)

C(20)C(21)

C(22)

C(18)C(17)

C(15)

Au(1) Au(2)

020

S(1)

S(2)

S(3)

S(4) S(6)

S(5)

H(19)

H(18)

H(10) H(13)

H(21)

H(22)

H(3)

H(6)

H(5)

H(2)C(3)

C(2)

C(1)C(6)

C(7)C(8)

C(9)

C(5)

C(4)

C(10)C(11)C(12)

C(13)

C(14)

C(16)C(19)

C(20)C(21)

C(22)

C(18)C(17)

C(15)

Au(1) Au(2)



000

020





000

020


119877 = 119866minus1

= (ℎ

21198902)(

1

119879119897

119879119903

119879119898

) =1291KΩ119879119897

119879119903

119879119898

(1)

where 119879119897

and 119879119903


119898





LUMO +2

LUMO +1

LUMO

HOMO

HOMO minus1

HOMO minus2


20

40

60

80

minus20

minus40

minus60

minus80

Applied voltage (V)

Curr

ent (120583

A)




119897

and 119879119903


119898


119879119898

= exp (minus120573119871) (2)


120573 = (1

ℏ) [2119898

lowast

120572120601]12

(3)


)1198980


4 Conclusion






000S(6)

S(1) S(2)

S(3)

S(4)

S(5)

H(5)

H(6)

H(2) H(19)

H(18)

H(10) H(13)

H(21)

H(22)

H(3)

C(1)C(2)

C(3)C(4)

C(5)C(6)

C(7)

C(10)C(11) C(12)

C(13)

C(14)

C(16)C(19)

C(20)C(21)

C(22)

C(18)C(17)

C(15)C(9)

C(8)

Au(1)

008

S(1) S(2)

S(3)

S(4) S(6)

S(5)

H(5)

H(6)

H(2) H(19)

H(18)

H(10) H(13)

H(21)

H(22)

H(3)

C(1)C(2)

C(3)C(4)

C(5)C(6)

C(7)

C(10)C(11) C(12)

C(13)

C(14)C(16)

C(19)C(20)C(21)

C(22)

C(18)C(17)

C(15)C(9)

C(8)

Au(1)

012

S(1)

S(2)

S(3)

S(4)

S(5)

H(5)

H(6)

H(2)

H(19)

H(18)

H(10)H(13)

H(21)

H(22)

H(3)

C(1)C(2)

C(3)C(4)

C(5)C(6)

C(7)

C(10)C(11) C(12)

C(13)

C(14)C(16) C(19)C(20)C(21)

C(22)

C(18)C(17)

C(15)C(9)

C(8)

Au(1)

S(6)

020S(1)

S(3) S(5)

S(4) S(6)

H(5)

H(6)

H(2)

H(18)

H(10) H(14)

H(21)

H(22)

H(3)

C(1)

C(2)C(3)

C(4)

C(5)C(6)

C(7)

C(10)C(11) C(12)

C(13)

C(14)C(16) C(17)

C(15)C(9)

C(8)

Au(1)




References




























3

OH)119899


























2

SiO4

fayalite Fe2

SiO4

and Co2

SiO4












































CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials






LUMO +2

LUMO +1

LUMO

HOMO

HOMO minus1

HOMO minus2


20

40

60

80

minus20

minus40

minus60

minus80

Applied voltage (V)

Curr

ent (120583

A)




119897

and 119879119903


119898


119879119898

= exp (minus120573119871) (2)


120573 = (1

ℏ) [2119898

lowast

120572120601]12

(3)


)1198980


4 Conclusion






000S(6)

S(1) S(2)

S(3)

S(4)

S(5)

H(5)

H(6)

H(2) H(19)

H(18)

H(10) H(13)

H(21)

H(22)

H(3)

C(1)C(2)

C(3)C(4)

C(5)C(6)

C(7)

C(10)C(11) C(12)

C(13)

C(14)

C(16)C(19)

C(20)C(21)

C(22)

C(18)C(17)

C(15)C(9)

C(8)

Au(1)

008

S(1) S(2)

S(3)

S(4) S(6)

S(5)

H(5)

H(6)

H(2) H(19)

H(18)

H(10) H(13)

H(21)

H(22)

H(3)

C(1)C(2)

C(3)C(4)

C(5)C(6)

C(7)

C(10)C(11) C(12)

C(13)

C(14)C(16)

C(19)C(20)C(21)

C(22)

C(18)C(17)

C(15)C(9)

C(8)

Au(1)

012

S(1)

S(2)

S(3)

S(4)

S(5)

H(5)

H(6)

H(2)

H(19)

H(18)

H(10)H(13)

H(21)

H(22)

H(3)

C(1)C(2)

C(3)C(4)

C(5)C(6)

C(7)

C(10)C(11) C(12)

C(13)

C(14)C(16) C(19)C(20)C(21)

C(22)

C(18)C(17)

C(15)C(9)

C(8)

Au(1)

S(6)

020S(1)

S(3) S(5)

S(4) S(6)

H(5)

H(6)

H(2)

H(18)

H(10) H(14)

H(21)

H(22)

H(3)

C(1)

C(2)C(3)

C(4)

C(5)C(6)

C(7)

C(10)C(11) C(12)

C(13)

C(14)C(16) C(17)

C(15)C(9)

C(8)

Au(1)




References




























3

OH)119899


























2

SiO4

fayalite Fe2

SiO4

and Co2

SiO4












































CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials






000S(6)

S(1) S(2)

S(3)

S(4)

S(5)

H(5)

H(6)

H(2) H(19)

H(18)

H(10) H(13)

H(21)

H(22)

H(3)

C(1)C(2)

C(3)C(4)

C(5)C(6)

C(7)

C(10)C(11) C(12)

C(13)

C(14)

C(16)C(19)

C(20)C(21)

C(22)

C(18)C(17)

C(15)C(9)

C(8)

Au(1)

008

S(1) S(2)

S(3)

S(4) S(6)

S(5)

H(5)

H(6)

H(2) H(19)

H(18)

H(10) H(13)

H(21)

H(22)

H(3)

C(1)C(2)

C(3)C(4)

C(5)C(6)

C(7)

C(10)C(11) C(12)

C(13)

C(14)C(16)

C(19)C(20)C(21)

C(22)

C(18)C(17)

C(15)C(9)

C(8)

Au(1)

012

S(1)

S(2)

S(3)

S(4)

S(5)

H(5)

H(6)

H(2)

H(19)

H(18)

H(10)H(13)

H(21)

H(22)

H(3)

C(1)C(2)

C(3)C(4)

C(5)C(6)

C(7)

C(10)C(11) C(12)

C(13)

C(14)C(16) C(19)C(20)C(21)

C(22)

C(18)C(17)

C(15)C(9)

C(8)

Au(1)

S(6)

020S(1)

S(3) S(5)

S(4) S(6)

H(5)

H(6)

H(2)

H(18)

H(10) H(14)

H(21)

H(22)

H(3)

C(1)

C(2)C(3)

C(4)

C(5)C(6)

C(7)

C(10)C(11) C(12)

C(13)

C(14)C(16) C(17)

C(15)C(9)

C(8)

Au(1)




References




























3

OH)119899


























2

SiO4

fayalite Fe2

SiO4

and Co2

SiO4












































CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials



























3

OH)119899


























2

SiO4

fayalite Fe2

SiO4

and Co2

SiO4












































CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials















2

SiO4

fayalite Fe2

SiO4

and Co2

SiO4












































CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials
























CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials



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