Towards accurate exchange-correlation potentials for molecules

The method of Zhao and Parr has been used to determine exchange-correlation potentials for molecular systems. Commencing with high-accuracy electron densities, determined from coupled-cluster calculations using Gaussian basis functions, the Zhao-Parr equations have been solved for large-value Lagrange multipliers. Calculations are reported for HF and N-2. The exchange-correlation potential surface is plotted, and the Kohn-Sham eigenvalues epsilon(i) are determined. In the two cases studied, epsilon(HOMO) is close to the negative of the ionisation energy.