The exchange energy of H +2 calculated from the exact first-order wavefunction of polarization perturbation theory

Abstract

The exact analytic first-order wavefunction of an H atom in the field of a proton obtained from the unsymmetrized perturbation theory as calculated in 1957 by Dalgarno and Lynn is used to calculate the exchange energy of H + 2 with the Holstein-Herring method. The asymptotic exchange energy obtained from the exact wavefunction is term-by-term identical with that obtained from the 1/ R expanded wavefunction and is within 5% of the exact exchange energy from large R down to R = 5 a 0.