Multiconfiguration Nonclassical-Energy Functional Theory*

Kohn-Sham theory (KST) is in principle applicable to both weakly correlated and strongly correlated systems, where the latter are systems that are not well represented by a single electron configuration. However, experience shows that KST is generally more accurate for weakly correlated systems. For strongly correlated systems, KST often leads to unphysical spin densities to make up for the deficiencies of its single-configuration representation of the electron density. A better way to handle densities due to multiconfiguration wave functions is to use explicitly multiconfigurational reference states. This has been done previously in multiconfiguration pair-density functional theory. In this lecture, I plan to discuss more general ways to model the nonclassical energy density in terms of the features of multiconfiguration wave functions.