Chemical bonding

Partial Density Of States (PDOS)

Charge density distribution

Charge transfer plot

Energy projected charge density

Electron Localization Function (ELF)

Crystal Orbital Hamilton Population analysis (COHP)

Mulliken population analysis

Born effective charge analysis

Bader topological analysis

Bonding Character in Materials

Ionic

Covalent

Metallic

The different types of bonding is strongly dependent on the electronic structure.

Electron Localization Function (ELF)

ELF becomes 1 either for

– perfect covalent bond

- lone paired electron

In homogenious electron gas the ELF is 0.5

- metallic bond

Charge transfer plot

∆ρ(r) = ρ(r) comp. - ρ(r)o.f.a

NaCl

Na Cl

In pure ionic solids,

electrons are completely

transferred from electro-positive

atom to electronegative atom.

Ionic bonding

Charge difference ELF

C in diamond structure

As opposed to ionic bonding in

which a complete transfer of

electrons occurs, covalent

bonding occurs when two (or

more) elements share their

electrons.

Charge density Charge difference ELF

Covalent bonding

Na

The valence electrons are

homogeneously distributed in the

space in between the atoms.

Charge density Charge difference ELF

Metallic bonding

LiH Li H

Ionic hydrides

Charge density Charge difference ELF

B2H6

B

H

Covalent Hydrides

Charge density Ch. diff. ELF

ScH2

Sc

H

Metallic Hydrides

Density Of States

Bonding nature in complex hydrides

Ex. LiAlH4

Li3AlH6

Interaction between Li - [AlH4] ionic

Interaction between Al – H within [AlH4]

covalent

ionic Li+Al3+ H4–

?

LiAlH4

Pure Ionic - A. Aguayo, D.J. Singh, Phys. Rev. B 69 155103 (2004)

−10 −7.5 −5 −2.5 0 2.5 5 7.5 10

1

2

3

4

0.1

0.2

0.2

0.4

0.6

0.8

0.1

0.2

0.3H

Al

Li

Total

EF

Energy (eV)

DO

S (

sta

tes

eV−

1)Non-metal

Energitically degenerated

Al – s and H – s states

Possible covalent type of interaction ?

DOS for Li3AlH6; s- states are shaded

DOS for Li3AlH6

ELF

0.50

0.75

0.100.20

0.05

0.01 -0.10

(a) (b) (c)

0.01 0.15

0.10 0.0

-0.01 0.25

1.0

0.001

H

Al Al

H

Al

H HLiLi

H

LiH

Charge density Charge transfer

Chemical bonding in Li3AlH6

−10 −7.5 −5 −2.5 0 2.5 5 7.5 10

1

2

3

4

0.1

0.2

0.2

0.4

0.6

0.8

0.1

0.2

0.3H

Al

Li

Total

EF

Energy (eV)

DO

S (

state

s eV

−1)

Energy projected (-7.5 to -6 eV) charge

density plot in Li3AlH6

Al-H 0.107

Li-H -0.014

2.000

10.968

1.844

Li

Al

H

Li3AlH

6

Al-H 0.173

Li-H -0.015

2.000

11.001

1.738

Li

Al

H

LiAlH4

Al-H 0.091 10.782

1.739

Al

H

AlH3

Be-H 0.045 2.366

1.822

Be

H

BeH2

Mg-H -0.04010.135

1.933

Mg

H

MgH2

C-H 0.384 6.256

0.936

C

H

CH4

Li-H -0.0082.014

1.986

Li

H

LiH

OVPOP(AB) M.CHARGEATOMSystem

Mulliken population analysis for selected hydrogen content compounds

0.1250.1160.1530.2100.125-0.088-0.817-0.831-0.911Z(H2)

0.0270.073-0.190-0.1740.0270.082-0.846-0.738-1.018Z(H1)

-0.0010.000-0.0010.000-0.0010.0341.7352.2372.237Z(Al)

0.1020.0240.0610.0140.1020.0170.9850.9570.99Z(Li)

yxzyxzzxyzxyzzyyxx

Calculated-Born-effective-charge tensor elements

(Z*) for the constituents of Li3AlH6

Chemical Bonding in Li3AlH6

- interaction between Li and [AlH4]- is ionic.

- bonding charecter of Al and H within [AlH4]- is a mixure of

ionic and covalent.

Bonding interaction in complex hydrides are not simple ionic or covalent

character but the mixture of them.