Orbital-polarization terms: from a phenomenological to a first-principles description of orbital magnetism in density-functional theory

摘要

Phenomenological orbital-polarization (OP) terms have been repeatedlyintroduced in the single-particle equations of spin-density-functional theory,in order to improve the description of orbital magnetic moments in systemscontaining transition metal ions. Here we show that these ad hoc correctionscan be interpreted as approximations to the exchange-correlation vectorpotential A_xc of current-density-functional theory (CDFT). This connectionprovides additional information on both approaches: Phenomenological OP termsare connected to first-principles theory, leading to a rationale for theirempirical success and a reassessment of their limitations and theapproximations made in their derivation. Conversely, the connection of OP termswith CDFT leads to a set of simple approximations to the CDFT potential A_xc,with a number of desirable features that are absent from electron-gas-basedfunctionals.