Dielectric constant of NiO and LDA+U

The local density approximation (LDA) and generalized gradient approximations (GGA) of density functional theory systematically overestimate the electronic polarizability of materials. We calculate the dielectric constant of NiO by the direct method and find, contrary to previous suggestions, that the LDA+U method reduces the polarization such that É_∞ decreases monotonically with increasing U. We illustrate the existence of a linear term in the effective exchange-correlation potential that counteracts the external electric field, thus demonstrating that the decrease of ε_∞ is intrinsic to the LDA+U correction. The reduction of the polarization is due mostly to reduced orbital mixing between the unoccupied e_g states and the occupied 2p states. Our work establishes LDA+U as a viable method for calculating the dielectric constants of correlated materials.