An approximate density matrix energy functional

Abstract

Several authors have shown that there exists an energy functional based on the one-matrix of an atomic or molecular ground state; this functional has been contrasted with energy functionals based on the two-matrix. Based on earlier work of Slater and Lowdin it is shown that the commutation rules satisfied by an approximate energy functional are just those satisfied by the exact functional. Thus there exists a known energy functional which is dependent on the one-matrix. For an idempotent density matrix this is the energy functional proposed originally by Slater.