Relativistic calculation of correlational energy for a helium-like atom

An analytical method is formulated for calculating the first-order correlational energy from the electron interaction, taking account of lag effects. Explicit analytical expressions are obtained for radial matrix elements. The nonrelativistic limit is investigated.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 10, pp. 33–35, October, 1985.