Post on 05-Jan-2016
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Applications III: Excited States, Solutions, Surfaces
Lecture CompChem 7Chemistry 347Hope 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