CORRELATION-ENERGY DENSITY FROM AB-INITIO FIRST-ORDER AND 2ND-ORDER DENSITY-MATRICES - A BENCHMARK FOR APPROXIMATE FUNCTIONALS

A procedure has been proposed to construct numerically the exchange-co rrelation epsilon(XC)(r) and correlation epsilon(C)(r) energy densitie s of density functional theory using the correlated first- and second- order density matrices from ab initio calculations, epsilon(C)(r) as w ell as its kinetic and potential components have been obtained for the two-electron He atom acid H-2 molecule. The way various correlation e ffects manifest themselves in the form of epsilon(C)(r) has been studi ed. The epsilon(C)(r) have been compared with some density functional local and gradient-corrected models epsilon(C)(mod)(r). The investigat ion of the shape of the model energy densities epsilon(C)(mod)(r) has been extended to the Be-2 and F-2 molecules and the corresponding corr elation energies E(C) have been calculated and discussed for a number of atomic and molecular systems. The results show the importance of a proper modeling of E(C)(r) in the molecular bond midpoint region. (C) 1995 American Institute of Physics.