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Applications I: Partial Charges and Potential Energy Surface Scans

Applications I: Partial Charges and Potential Energy Surface Scans. Lecture CompChem 5 Chemistry 347 Hope College. Previous Applications. Geometry optimization Conformation stability Transition states IR and NMR spectra Thermochemistry (ZPE, C V , S, H, G) Enthalpies of reaction D rxn H.

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Applications I: Partial Charges and Potential Energy Surface Scans

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

  2. Previous Applications • Geometry optimization • Conformation stability • Transition states • IR and NMR spectra • Thermochemistry (ZPE, CV, S, H, G) • Enthalpies of reaction DrxnH

  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)

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