Shaun Williams

1. The Coe Group Shaun Williams Kenneth Rodriguez Shannon Teeters- Kennedy Summit Shah Alexandra Sudnitsyn Frank Hrovat Katie Cilwa You have two PCs at your disposal in EL 0051. Coe Group Members can let you in when I’m not around.

2. Kenneth Rodriguez Read Ch. 2 of Ken’s MS thesis (available as a pdf file) for an overview of computational chemistry

3. Hyperchem 7.5 is available in EL 051

4. To calculate the energy of an atomic or molecular system you have to choose between a multitude of methods. In Hyperchem, you start at the “Setup” menu …

5. Models of molecules and their interactions - molecules often modeled by point charges, interactions by model force fields • Least sophisticated treatment • Can do largest systems Forcefields in Hyperchem

6. Quantum mechanical treatment with shortcuts in the evaluation of 4-index (Coulomb and Exchange) integrals • Better than MM, not as good as ab initio • Can do larger systems than ab initio • Only valence electrons Semi-empirical methods in Hyperchem These integrals are assigned values by empirical relationships rather than evaluation

7. Quantum mechanical treatments from 1st principles • Ab initio is Latin for “from the beginning” • Different levels of approximation • Best calculations, but most computationally intensive Hyperchem has full HF, but only single point MP2 Chapter 2, Kenneth Rodriguez, OSU Masters Thesis, 2005 Cramer, C.J., Essentials of Computational Chemistry, Theories and Models. 2002 ed. 2002, Southern Gate, Chichester, West Sussex: John Wiley & Sons, LTD.

8. Quantum mechanical treatment based on electron density rather than orbitals • Allows direct treatment of electron correlation, but no theoretical forms for these functionals • Can be as rigorous as ab initio, but generally isn’t • Often less computationally intensive than ab initio approach B3LYP gets electron density from orbitals like HF, but has an empirical form for electron correlation, actually has a little too much electron correlation

9. Hartree Fock - the Simplest Ab Initio Theory wavefunction is product of orbitals that each satisfy Schroedinger equation where the energy operator is producing matrix elements energy of each electron in average field of other electrons Giving 4-index integrals Gaussians Chapter 2, Kenneth Rodriguez, OSU Masters Thesis, 2005 Cramer, C.J., Essentials of Computational Chemistry, Theories and Models. 2002 ed. 2002, Southern Gate, Chichester, West Sussex: John Wiley & Sons, LTD.

10. Relation of Ab Initio Energetics to Experiment nC(g)+mH(g)CnHm(g) From Experiments From Ab Initio Calculations normal mode analysis gives ZPE and thermal corrections to go between

11. aestimated with harmonic approximation for vibrations, scaling factor of 0.8929 from a HF/6-31G* calc. bmethod not variational, an unknown electron-correlation term has been added to the real Hamiltonian

12. HF<MP2~CCD<CISD<MP4SDQ~QCISD~CCSD<MP4<QCISD(T)~CCSD(T) Several electronic computational methods cost of CPU by a form of scaling behaviors as a function of basis sets, N. Note the values in this table were taken from Cramer[2].

13. Gaussian03 and Gaussview are now licensed on campus for PCs. If you are in a research group, you can get each program on a CD for $5 each at 512 Baker Systems Engineering. large range of ab initio and DFT methods, a compendium of generations of work

15. Example of inputting a simple molecule and doing calculations

16. PDF files