Optimized effective potential method based on spin-resolved components of the second-order correlation energy in density functional theory

A correlated optimized effective potential method based on scaled-opposite-spin second-order correlation (OEP2-SOS) is presented. This approach is based on the finding that the same-spin- and opposite-spin-correlation potentials are almost proportional to each other at each point in the real space. The performance of the OEP2-SOS method is validated for benchmark atomic and molecular systems, and we find that all the OEP2-SOS results largely outperform those from second-order Görling-Levy perturbation theory and, additionally, the presented method can converge also when quasidegeneracy is present (e.g., in the Beryllium atom). The OEP2-SOS approach is thus an accurate and efficient method to supplement exact exchange with an ab initio correlation and, importantly, with small additional computational cost.