Accuracy of the Krieger-Li-Iafrate approximation for molecules

Accurate electronic structure calculations for diatomic molecules have been performed, using the Krieger-Li-Iafrate (KLI) approximation to the optimized potential method (OPM) for the evaluation of the exact exchange potential of density-functional theory. It is found that the KLI scheme provides an excellent approximation to the full OPM for these systems. The deviations between both variants of the OPM are smaller than the differences resulting from the use of different basis sets. Furthermore, it is shown that the spectroscopic constants obtained with the exchange-only KLI approach are very close to Hartree-Fock values.