GRADIENT CORRECTION TO THE EXCHANGE PAIR-CORRELATION FUNCTION OF THE WEIGHTED SPIN-DENSITY APPROXIMATION IN THE DENSITY-FUNCTIONAL FORMALISM

A gradient correction to the exchange pair-correlation function G(x si gma)(hom)(r(12)) of the homogeneous electron gas is developed in order to improve its performance for inhomogeneous systems within the weigh ted spin-density approximation (WSDA) of density functional theory. Th e correction factor has the form of a Pade-type approximant of the dim ensionless gradient \del n(sigma)(r)\/n(sigma)(4/3)(r) (n(sigma) the e lectron spin-density) and of the dimensionless argument (k) over tilde (F sigma)(r(perpendicular to))r(12) ((k) over tilde(F sigma) is the we ighted spin-density Fermi momentum and r,, is the interelectronic dist ance). In the zero-gradient Limit the corrected pair-correlation funct ion reduces to G(x sigma)(hom), while for atoms the present WSDA with gradient correction (WSDA-GC) provides a substantial improvement of th e calculated exchange energies compared to the standard WSDA based on G(x sigma)(hom). (C) 1998 Elsevier Science B.V. All rights reserved.