Core and valence regions of molecules

In real space, the partitioning of a molecule into valence and core regions is rooted in the picture of `valence electrons' in the field of `effective cores' consisting of nuclei partially shielded by inner-shell `core' electrons. The appropriate valence kinetic and potential energies, T ^v and V ^v, respectively, are obtained by subtracting the pertinent parts associated with the cores from the corresponding conventional total T and V energies but, far from T ^v+V ^v, the physically correct valence-region energy is . This result differs markedly from T ^v+V ^v because E ^v, T ^v and V ^v do not obey the virial theorem. Received: 21 August 1996 / Accepted: 14 November 1996