1. Applications I: Partial Charges and Potential Energy Surface Scans Lecture CompChem 5 Chemistry 347 Hope College

2. Previous Applications Geometry optimization Conformation stability Transition states IR and NMR spectra Thermochemistry (ZPE, C V, S, H, G) Enthalpies of reaction  rxn H

3. Partial Charges No unique definition of assigning electrons to atoms Mulliken populations: derived from AO coefficients and overlap integrals Natural Bonding Orbitals: derived by assigning electrons to core, valence, and lone pair orbitals Electrostatic potential-derived charges: derived to match electrostatic potential at a given distance

4. Rigid Potential Energy Surface Scan SCAN keyword Series of Single Point calculations that systematically vary one (or more) coordinate Non-stepped coordinates are fixed, not optimized Relatively fast, but of limited utility

5. Relaxed Potential Energy Surface Scan Opt=Z-matrix or Opt=AddRedundant keyword A series of Optimize Geometry calculations that systematically vary one (or more) coordinate Stepped coordinate must be carefully chosen to represent chemical feature of interest Available in Z-matrix (easier input file) or redundant coordinates (more robust method)