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The exchange potential in solids is approximated by a modification of the original Slater formula for a freeelectron gas. The procedure, based on a uniform-electrongas approximation for local regions, modifies the Slater calculation to include the influence of electron correlation on pair interactions and, therefore, decreases the potential sharply in regions of low density. Moreover, at nearly all densities this correlation introduces a correction factor sufficiently severe to make itself felt in any calculation in which the choice of exchange potential is important. The approximation consists, in effect, of replacing the Coulomb interaction e/sup 2//r/sub 12/ in the original Slater treatment of exchange by (e/sup 2//r/sub 12/ x exp (-k/sub s/r/sub 12/), where K/ sub s/ is an a ppropriate screening factor. (H.D.R.)
Robinson et al. (Sat,) studied this question.