A wave function was obtained for the ${}_{}{}^2{}_{}{}^{}S$ ground state of the lithium atom using 60 basis functions of the Hylleraas type, i.e., with interelectronic distance coordinates. The energy obtained was -7.478025 atomic units as compared with the value -7.478069 calculated from experiments. The wave function was used to calculate the Fermi contact term. It was found that this basis set gave the value 2.906, which is in agreement with experiments, when both doublet spin functions were used, but a value that was 4% greater when only one spin function was used. In the first case, 100, and in the latter, 60, linear parameters were varied. The interelectronic distance coordinates are expanded according to a formula by Sack. The final integrals are evaluated analytically, and the resulting formulas, along with a short discussion of their convergence properties, are given in an Appendix.

• Received 11 December 1967

DOI:https://doi.org/10.1103/PhysRev.169.49