Molecular Models

Empirical/Molecular Modeling Semi Empirical Ab Initio/DFT

Neglect ElectronsNeglect Core Electrons

Approximate/parameterize HF IntegralsFull Accounting of Electrons

Molecular Models

Methodology: Hamiltonian

TermValue (hartrees)

% Total

Kinetic E 99.85594 -100%

N-E Attraction

-250.58398 251%

E-E Repulsion (+Exchange)

45.49697 -46%

N-N Repulsion

5.22817 -5%

Total -100.00290 1001 Hartree= 627 kcal/mol

Theory: Energy

Approximations:Huckel MO

Approximations:Semi-empirical Methods

drrij ij Overlap alDifferenti

** )2()2(1

)1()1(

and

center atomic sameon are and

center atomic sameon are and

CNDO

NNDO

Approximations:Wavefunction

Computation: Basis Set

AO Type

Functional Forms

s e-ar2

Px x e-ar2

Py y e-ar2

Pz z e-ar2

dx2 x2 e-ar2

dy2 y2 e-ar2

dz2 z2 e-ar2

dxy xy e-ar2

dxz xz e-ar2

dyz yz e-ar2

Computation: Basis Set

Basis set# functions

Basis set# functions

Basis set# functions

STO-3G 5 6-31G 9 6-311G 13

3-21G 9 6-31G* 15 6-311G* 18*

4-31G 9 6-31+G* 19 6-311+G* 22*

Computation: Electron Correlation

Molecular Models

Empirical/Molecular Modeling Semi Empirical Ab Initio/DFT

Neglect ElectronsNeglect Core Electrons

Approximate/parameterize HF IntegralsFull Accounting of Electrons

HT EHT CNDO MINDO NDDO MNDO HF

Completeness

Conclusion