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Molecular Models. Methodology: Modify Wavefunction.

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Presentation on theme: "Molecular Models. Methodology: Modify Wavefunction."— Presentation transcript:

1 Molecular Models

2 Methodology: Modify Wavefunction

3 Theory: Wavefunction

4 Computation: Basis Set AO TypeFunctional Forms s e -ar 2 Px x e -ar 2 Py y e -ar 2 Pz z e -ar 2 dx2dx2 x 2 e -ar 2 dy2dy2 y 2 e -ar 2 dz2dz2 z 2 e -ar 2 d xyxy e -ar 2 d xzxz e -ar 2 d yzyz e -ar 2

5 Computation: Basis Set Basis set # functions Basis set # functions Basis set # functions STO-3G56-31G96-311G G96-31G* G*18* 4-31G96-31+G* G*22*

6 Computation: Electron Correlation

7 Configuration Interaction (CI) unoccupied occupied

8 Moller Plesset (MP) Hartree-Fock close to Full Hamiltonian Perturbation

9 Computation: Computation Time

10 Results: Geometry Basis Bond Length Error (Å) Bond Angle Error (deg.) STO-3G G G(*) G* G** G** Mean Absolute Errors for A-H bond parameters Basis Bond Length Error (Å) (single bonds) Bond Length Error (Å) (multipe bonds) Bond Angle Error (deg.) STO-3G G G(*) G* G** G** Mean Errors for A-B bond parameters

11 Results: Geometry MoleculeCoordinateHFMP2CCSDMP4CCSD(T) Error in Bond Length (Å) H2OH2OO-H NH 3 N-H CH 4 C-H C2H2C2H2 C-H C-C CH 2 O C-H C=O HCN C-H C-N HCN N-H C-N CO 2 C-O Average Abs. Error () Error in Bond Angle (deg.) H2OH2OH-O-H NH 3 H-N-H CH 2 0H-C-O Average Error (deg.)

12 Results: Geometry

13 Results: Energy

14 Methodsto-3g3-21Gd954-31G4-31g*4-31g**6-31G6-31G* 6- 31G** G** G** (3df,2p d) cc-pvdzcc-pvtzcc-pvqc # Basis fumctions: UHF RHF MP MP MP4D MP4DQ MP4SDTQ MP NA GVB/RO HF CCSD CCSD(T) CID CISD QCISD QCISD(T) BLYP ROBLYP Singlet-Triplet Splittings (kcal/mole): E exp = 9.2 kcal/mole

15 Results: Energy Reaction HF/6-31FG** //HF6- 31G* MP2/6-31G** //MP2/6-31G* MP3/6-31G** //MP3/6-31G* MP4/6-31G** //MP4/6-31G* Expt. H 2 ->H*+H* Li->Li*+H* BeH->Be*+H* ,56 BH->B*+H* CH*->C+H*(2) CH*->C+H*(4-) NH->N*+H* ,<85 OH*->O+H* FH->F*+H* BH 2 *->BH+H* CH 2 ->CH*+H*( 3 B 1 ) ,106 CH 2 ->CH*+H*( 1 A 1 ) NH 2 *->NH+H* OH 2 ->OH*+H* BH 3 ->BH 2 *+H* CH 3 *->CH 2 +H* NH 3 ->NH 2 *+H* CH 4 ->CH 3 *+H*

16 Results: Energy

17 Results: Charge Example: Chlorine atomic charge in CH 3 Cl, HF Mulliken and NPA charges ; calculated with many basis sets (at the HF/6-31G* optimized geometry).

18 Problems: BSSE Basis Set Superposition Error MoleculesMethod BSSE kcal/mol HF+HF HF/6-31+G* MP2/6-31+G* H 2 +NH 3 HF/DZP0.65 (CH 3 COOH) 2 HF/6-31G* MP2/6-31G*

19 Problems: Size Consistency

20 Problems: UHF Instability Method E relative (Anthracene- Phenanthrene) UHF/6-31G*1.42 RHF/6-31G*6.88 MP2/6-31G**7.09 MP3/6-31G6.17 MP4(SDQ)/6-31G6.48 CISD/DZ7.49 CCSD6.32 CCSD(T)5.98

21 Problems:Variational Principle


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