SIMPLIFIED ACCURATE APPROXIMATION FOR THE KOHN-SHAM POTENTIAL USING THE KLI METHOD

The method of Krieger, Li, and Iafrate (KLI) [Phys. Rev. A46, 5453 (19 92) and A47, 165 (1993)] is employed to calculate the Kohn-Sham (KS) p otential, V-x sigma, for the exchange-only case in which the electron- electron interaction between ''core'' electrons in the Hartree-Fock ex change energy functional is treated in the local-spin-density (LSD) ap proximation with and without self-interaction-correction (SIG). The re sulting V-x sigma(r) maintains the important analytic properties exhib ited by the exact KS potential. When the core is taken to include all occupied states except those in the last two occupied subshells of the atom, we find that properties strongly dependent on the valence elect ron states continue to be accurately approximated. In particular, when the LSDSIC approximation is employed, we find the results of self-con sistent calculations of the ionization potential and electron affinity are within 0.3 mRy of the exact KS results and that the energy eigenv alue corresponding to the highest energy occupied orbital and [r(2)] h ave an average error of a few tenths of 1% for both atoms and negative ions for Z less than or equal to 20. Similarly, slightly less accurat e results are obtained when the LSD approximation is employed. These r esults suggest that the KLI method may be accurately and more easily a pplied to multiatom systems when this additional approximation is made . (C) 1997 John Wiley & Sons, Inc.