this talk has only three equationsJiahao ChenVieques, PR

http://mfrost.typepad.com/cute_overload/2006/05/bullblob.html

qtpie: how cute can you get?

http://mfrost.typepad.com/cute_overload/2006/02/peeky_mcpeekers.html

http://mfrost.typepad.com/cute_overload/2006/02/peeky_mcpeekers.html

molecular mechanics and electronic structure

• In MM, electronic structure changes nuclear geometry

• How do nuclear changes affect electronic structure?

• Conventional answer: they don’t• Better answer: polarizable charge

models

http://mfrost.typepad.com/cute_overload/2006/02/peeky_mcpeekers.html

electronegativity and hardness

• Atoms in molecules = thermodynamic systems in contact with external particle bath

N, V, T

i

Ei qi

EA

IP2

Ni = Zi - qi

00

http://www.flickr.com/photos/fantasyfan/35417428

how qtpie works

charge vs. charge transfer variables

q5q4

QEq

q3

q2

q1 p12

p23

p34

p45

QTPIE

results

• dissociating NaCl– problem in QEq– finite charge separation

when dissociated– divergent dipole

moment

• parameters transferable– H2O for various

geometries– suddenly dissociated

NaCl.6H2O

dipole polarizabilities• Severely overestimated in QEq• Less severely so in QTPIE, but still bad!

System QEq QTPIEMP2/STO-

3GMP2/3Z

NaCl13.9474

0.00000.0000

6.21710.00000.0000

1.21080.13910.1390

4.79574.13844.1375

H2O3.46531.23170.0000

1.83380.65160.0000

0.80090.42080.0052

1.52691.45661.4333

Phenol24.624420.3270

0.0000

13.029810.7566

0.0000

8.42407.04880.8595

13.675812.3622

6.9981

where it’s going

• rewriting in scientific python• reparameterization, e.g. using DFTB

results• QTPIE/MM method

– to interface with MDX, a MD library– study solvated electrons

http://www.flickr.com/photos/fantasyfan/33736090

open questions: treating multiple states

charged systems are really hard

• Lagrange multipliers v. reparameterization

• e.g.: Na : water : phenol -stacked system

qNa/e QEq QTPIE

Lagrange

0.6177 0.1876

reparam.

0.4798 0.8648

Lagrange multiplier method

reparameterize Na: account for formal charge

C2 C1

C3

C4C5

C6 O7

H11

Na17

H14

H15 H16

H13 H12

O8

H9 H10

Mulliken/MP2/cc-pVDZ charge: 0.7394

still needs brainstorming

• Charge distributions for excited states• Theoretical interpretation as coarse-

grained quantum mechanical theory?– Intuitively connected to DFT– Statistical mechanical interpretation of

energy function

• QM definition for charge?– Proposal: charge needed to define

electrostatic force that best approximates the Hellman-Feynman force

interlude

icqc 2006, kyoto

makemovie visualizes orbital changes along a trajectory

visualization scripts

Aromaticity and scattering on a ring

• Crude model:– Substituents = ideal

metals with well-defined Fermi wavevectors

– Aromatic ring = benzene

• Switching behavior of meta-coupled benzene derivatives– transmission probability

triples from ground to first excited states

R1

R2

http://mfrost.typepad.com/cute_overload/2006/06/perfect_ear_flo.html

Any questions?