Tight constraints on the exchange-correlation potentials of degenerate states.
Identities for the difference of exchange-correlation potentials and energies in degenerate and nondegenerate ground states are derived. The constraints are strong for degenerate ground states, and suggest that local and semilocal approximations to the exchange-correlation energy functional are incapable of correctly treating degenerate ground states. For degenerate states, it is possible to provide both local (pointwise) equality and global inequality constraints for the exchange-correlation potential in terms of the Coulomb potential.
Department of Chemistry and Chemical Biology, McMaster University, Hamilton, Ontario L8S4M1, Canada.
Paul W
PW
Ayers
Department of Chemistry, Duke University, Durham, North Carlina 27708, USA.
Mel
M
Levy