SEPARATION OF THE EXCHANGE-CORRELATION POTENTIAL INTO EXCHANGE PLUS CORRELATION - AN OPTIMIZED EFFECTIVE POTENTIAL APPROACH

Most approximate exchange-correlation functionals used within density- functional theory are constructed as the sum of two distinct contribut ions for exchange and correlation. Separating the exchange component f rom the entire functional is useful since, for exchange, exact relatio ns exist under uniform density scaling and spin scaling. In the past, accurate exchange-correlation potentials have been generated from esse ntially exact densities but they have not been correctly decomposed in to their separate exchange and correlation components (except for two- electron systems). Using a recently proposed method, equivalent to the solution of an optimized effective potential problem with the corresp onding orbitals replaced by the exact Kohn-Sham orbitals, we obtain th e separation according to the density functional theory definition. We compare the results for the Ne and Be atoms with those obtained by th e previously used approximate separation scheme.