CORRELATION POTENTIALS FOR THE HE ATOM AND THE HYDROGEN MOLECULE - A COMPARISON BETWEEN THE CORRELATION FACTOR APPROACH AND DFT CORRELATION-ENERGY FUNCTIONALS

Two points about correlation potentials have been dealt with in this a rticle. The first one is related to the shape of some of the most repr esentative correlation potentials applied to the ground state of the H e atom. It is shown here that both LDA and two-body density correlatio n potentials compare well with that obtained through the quantum chemi stry definition of correlation energy. This is an interesting result b ecause, in previous works, it had been shown that none of the correlat ion potentials compared well with the Kohn-Sham one. The gradient-corr ected correlation potentials exhibit a very different behavior to that of both exact potentials (quantum chemistry and Kohn-Sham ones). The other question posed here refers to how a reference to the two-body de nsity must modify DFT functionals for the correlation energy, when a m ultideterminant wave function is needed. This question has been addres sed by analyzing the variation of correlation potentials as the bond l ength of the H-2 molecule increases. The results show that an external reference to the two-body density qualitatively improves DFT correlat ion potentials and also that only those functionals explicitly dependi ng on two-body density can give the quantitative correct trends. (C) 1 998 John Wiley & Sons, Inc.