DIFFERENCES BETWEEN AB-INITIO AND DENSITY-FUNCTIONAL ELECTRON-DENSITIES

We analyzed the energy contributions and the spatial distribution diff erences of several electron densities of atoms and small molecules. Th e results show the insensitivity of local spin density correlation fun ctionals in respect to differences in the electron densities. On the o ther hand, significant changes in one-electron and two-electron energy contributions are observed, although both compensate each other. The projection of the differences between these electron densities, referr ed to as the Hartree-Fock density, shows a qualitative resemblance bet ween multideterminantal and Kohn-Sham wavefunctions. Finally, a compar ative analysis of the optimized conformational parameters obtained usi ng several methods shows that the inclusion of the correlation energy in SCF or in post-SCF procedures gives similar results and that the ex change potential is more important than is the correlation potential t o improve these conformational parameters. (C) 1997 John Wiley & Sons, Inc.