title: Exchange methods in Kohn-Sham theory.
abstract: Differences between exchange methods in exchange-only Kohn-Sham theory are highlighted by calculations of diatomic molecule total energies, uncoupled isotropic NMR shieldings, and HOMO-LUMO eigenvalue differences. Optimised effective potential (OEP) and Wu-Yang (WY) results are very similar. Localised Hartree-Fock (LHF) and Krieger-Li-Iafrate (KLI) results are close to one another, but are different to OEP and WY. Becke 1988 exchange (B88X) is different again. Shieldings reduce from OEP/WY to LHF/KLI to B88X, which is consistent with an observed reduction in HOMO-LUMO gaps. LHF, KLI, and B88X shieldings and HOMO-LUMO gaps are closer to near-exact, correlated values, than are the OEP values. These variations arise entirely due to differences in the one-electron exchange potentials, which is clearly evident in potential difference plots, relative to OEP, for the N2 molecule. Density difference plots are also presented, which exhibit a spatial correlation with the potential differences. HOMO and LUMO probability density difference plots show a contraction of the LUMO relative to OEP, which is consistent with the NMR and HOMO-LUMO findings. Plots are also presented for near-exact, correlated Kohn-Sham calculations. The features are qualitatively similar to those observed in the LHF, KLI, and B88X plots, highlighting correlated character in these approximate exchange-only calculations.
authors.affiliation: Department of Chemistry, University of Durham, Durham, DH1 3LE, UK.
authors.forename: Andrew M
authors.initials: AM
authors.lastname: Teale
authors.forename: David J
authors.initials: DJ
authors.lastname: Tozer
mesh_terms: D000465:Algorithms; D003198:Computer Simulation; D004563:Electrochemistry / Q000379:methods*; D004579:Electron Transport; D004735:Energy Transfer; D009682:Magnetic Resonance Spectroscopy / Q000379:methods*; D008956:Models, Chemical; D011789:Quantum Theory; D055672:Static Electricity