Spurious interactions, and their correction, in the ensemble-Kohn-Sham scheme for excited States.

Abstract

We observe that the direct Coulomb (Hartree) term appearing in the ensemble-density-functional theory for excited states contains an unphysical ("ghost") interaction which has to be corrected by the ensemble exchange and correlation functional. We propose a simple additive correction to the conventional ensemble exchange energy in the form of an orbital functional. By treating this corrected exchange energy functional self-consistently within the optimized effective potential method one finds a significant improvement of atomic excitation energies.