ALTERNATIVE DENSITY-FUNCTIONAL THEORY FOR ATOMS AND MOLECULES

A reference state whose electronic density is not necessarily equal to the true ground-state density is used in theoretical methods for elec tronic correlation in atoms and molecules. Because the density functio nal theory of Kohn and Sham postulates a model system for which these two density functions are identical, this postulate appears to preclud e use of this model state as a reference state when formulating many-B ody corrections to the theory. This conflict is resolved by expressing the ground-state energy as a functional of the electronic density of a reference state determined by maximizing its projection on the true wavefunction.