Intergeminal Correction to the Antisymmetrized Product of Strongly Orthogonal Geminals Derived from the Extended Random Phase Approximation.

Abstract

We present a correction to the antisymmetrized product of strongly orthogonalized geminals (APSG) approach accounting for intergeminal correlation energy that APSG lacks. The correction is based on the fluctuation dissipation theorem formulated for geminals with transition density matrices obtained from the recently formulated extended random phase approximation. We show that the proposed intergeminal correlation correction greatly improves upon APSG energies by accounting for short- and long-range dynamical correlation. For covalently bonded molecules the potential energy curves are in good agreement with the exact results in the entire range of bond breaking. Also the description of weakly interacting systems is superior to that of APSG. In particular, we show that the proposed intergeminal correlation energy reduces to the correct form of the dispersion energy and asymptotically yields exact interaction energy of the helium dimer.