Alternative definition of exchange-correlation charge in density functional theory

A new definition of the exchange-correlation charge is presented. This charge is related to the exchange-correlation potential of density functional theory by the Poisson equation. It is illustrated how, using the Zhao–Morrison–Parr method, this new exchange-correlation charge can be evaluated numerically, thus providing direct input for the ongoing process of finding improved approximate density functionals. Several properties of this new charge, including the sum rule and Coulombic-like behavior, are derived. Both atomic shell and subshell structures are observed. Exchange-correlation charges generated from various approximate functionals are calculated and compared with numerically accurate data for a few atoms.