On variational principles in density and density matrix functional theories

Abstract

Variational principles in density and density matrix functional theories will be discussed for ground states and excited states. What is allowed and not allowed in principle will be analyzed. Then expansions for the exchange-correlation potential, as obtained from orbital dependent functionals, will be presented, and constraints for the exact potential will be studied. Then it will be observed that the Kohn-Sham kinetic energy can be expressed in terms of the density and a single orbital