Applications III - Hope College

Applications III: Excited States, Solutions, Surfaces Lecture CompChem 7 Chemistry 347 Hope College Excited State Methods Difficult to compute,as methods tend to find the ground state ZINDO: semi-empirical CIS (CI-Singles): fast, robust, qualitative

TD (Time Dependent): fast CASSCF (Complete Active Space SCF): slow, tricky, more accurate (full CI of a subset of orbitals) CIS Promote a single electron electron from occupied to unoccupied orbitals Wavefunctions are built up from these interacting electron configurations Lowest energy wavefunction is the ground

state; higher energy wavefunctions are excited states Energy differences between states correspond to electronic transitions in the UV-Vis spectrum Solution Methods Default calculations are gas phase (isolated molecule) Onsager (Dipole and spherical cavity) PCM (Polarized Continuum Model) atomic spheres

isodensity surface SCF isodensity surface COSMO (Conductor-like Screening Model) can compute energy derivatives Solution Calculations Solvent is characterized by their dielectric constant Water=78.4, acetonitrile=35.4, cycloheaxane=2.0

Solute is characterized by a molecular volume Esolvation = Esolution - Egas phase Ions are effectively solvated by polar solvents due to favorable ion-dipole electrostatic interactions Surfaces (MOViewer) Electron Density: 0.003 = size of molecule Electrostatic Potential: map EP onto ED using color code: red=negative blue=positive

Electrophilic Frontier Density: map HOMO density onto ED Nucleophilic Frontier Density: map LUMO density onto ED red =small blue = large

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