We develop a density-matrix correlation-energy functional suitable for treating impurity sites with strong electronic correlations. The functional is based on a rigorous theorem about the form of such functionals as well as an exact inequality for the exchange-correlation energy. It is validated by comparison with exact results for small clusters, and is used to treat the electronic properties of an Anderson impurity in a random alloy.

• Received 25 September 2000

DOI:https://doi.org/10.1103/PhysRevB.63.115116