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Tight constraints on the exchange-correlation potentials of degenerate states
1Department of Chemistry and Chemical Biology, McMaster University, Hamilton, Ontario L8S4M1, Canada.
Abstract:
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.
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