Atomic, Molecular, and Optical Physics Seminar
A Fresh Look At Density Functional Theory
IBM Almaden Research Center, San Jose, California
In the density functional theory of Kohn and Sham, the occupied orbital functions of a model state are derived by minimizing the ground-state energy functional of Hohenberg and Kohn. It has been assumed for some time that effective potentials in the orbital Kohn-Sham equations are always equivalent to local potential functions. When tested by accurate model calculations, this assumption is found to fail for more than two electrons. Here this failure is traced to the unjustified assumption that functional derivatives of any well-defined density functional necessarily exist in the form of multiplicative local potential functions. A deeper look at the relevant variational theory shows that this is not true. Instead, the fermion nature of interacting electrons implies a more general form of functional derivative, operationally equivalent to a linear operator that acts on orbital wave functions. When extended to include such nonlocal potentials, the theory is free of inconsistencies and paradoxes, formally exact, and explicitly related to standard many-body theory.
Monday, April 22, 2002
Gant Science Complex