CURRENT-DEPENDENT EXCHANGE-CORRELATION POTENTIAL FOR DYNAMICAL LINEAR-RESPONSE THEORY

The frequency-dependent exchange-correlation potential, which appears in the usual Kohn-Sham formulation of a time-dependent linear response problem, is a strongly nonlocal functional of the density, so that a consistent local density approximation generally does not exist. This problem can be avoided by choosing the current density as the basic va riable in a generalized Kohn-Sham theory. This theory admits a local a pproximation which, for fixed frequency, is exact in the Limit of slow ly varying densities and perturbing potentials.