The multiconfiguration approximations 1s2 - 1s2s, 1s2 - 1s2s - nl2 n 2, 3 l 0, 1, 2, and 1s2 - 1s2s - 2p2 - 3d2 - 3p2 are applied to the atomic species He, Li, and Be. It is shown that the two-configuration approximation 1s2 - 1s2s has a considerable effect if the orbitals of both the correction configuration and the configuration under study are determined in a two-configuration approximation. The energy value as calculated in a multiconfiguration approximation including the configuration 1s2s is about 0.010 esu lower than the multiconfiguration energy value calculated without allowance for the minimum configuration. The problem of the convergence of the multiconfiguration approximation is discussed. Author
Trans. of Vilna Univ. Mokslo Darbai (Lithuanian SSR), n16 Mathematikos, Fizikos ir Chemijos Mokslu Serija, n7 p93-104 1957, by Stuart W. Kellogg.