STRUCTURE OF THE OPTIMIZED EFFECTIVE KOHN-SHAM EXCHANGE POTENTIAL ANDITS GRADIENT APPROXIMATIONS

An analysis of the structure of the optimized effective Kohn-Sham exch ange potential upsilon(x) and its gradient approximations is presented . The potential is decomposed into the Slater potential upsilon(s) and the response of upsilon(s) to density variations, upsilon(resp). The latter exhibits peaks that reflect the atomic shell structure. Kohn-Sh am exchange potentials derived from current gradient approaches for th e exchange energy are shown to be quite reasonable for the Slater pote ntial, but they fail to approximate the response part, which leads to poor overall potentials. Improved potentials are constructed by a dire ct fit of upsilon(x) with a gradient-dependent Pade approximant form. The potentials obtained possess proper asymptotic and scaling properti es and reproduce the shell structure of the exact upsilon(x). (C) 1996 John Wiley & Sons, Inc.