Calculations on the 2S ground state of the lithium atom.

Extensive variational calculations on the $^{2}\mathrm{S}$ ground state of the lithium atom are reported. With use of a 352-term Hylleraas-type expansion, the nonrelativistic ground-state energy of $^{2}\mathrm{S}$ Li i is determined to be -7.478 058 a.u., which lies approximately 3 ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}1}$ above empirical estimates of the nonrelativistic ground-state energy. This variational upper bound to the ground-state energy is the lowest to our knowledge reported to date in the literature. A number of expectation values, including the individual energy terms, the Fermi-contact interaction, the electron density at the nucleus, and the moments 〈${r}_{i}^{n}$〉, n=1\char21{}3, and 〈${r}_{\mathrm{ij}}^{n}$〉, n=1,2, are also evaluated. The general rates of convergence of the calculation are discussed. The role played by the two doublet spin eigenfunctions is examined, and the importance of including both of these functions for the accurate calculation of the Fermi-contact interaction is discussed.