High precision calculations on the 2S ground state of the lithium atom

Abstract

The results of a detailed variational calculation on the 2 Sground state of the lithium atom are reported. The wave function was constructed using Hylleraas‐type functions with extensive exponent optimization being employed. The calculated nonrelativistic ground state energy obtained was −7.478 059 53 a.u., which is the lowest upper bound estimate for this quantity obtained to date. The discrepancy with semi‐empirical estimates of this quality is discussed. The hyperfine coupling constant for 7Li is calculated to be 401.795 MHz, which compares favorably with the experimental result of 401.752 043 3 MHz. Expectation values are reported for the individual energy components, as well as the electron density at the nucleus, and the specific mass shift operator. The transition isotope shift is also evaluated. The convergence characteristics of the calculations are discussed, along with the effect of retaining only one of the two possible spin eigenfunctions in the basis set.