Magnetic Hyperfine Structure of Lithium, Using an Approximate Projected Hartree-Fock Method

An approximate projected Hartree-Fock calculation is performed for the $^{2}S$ ground state of the Li atom. It is shown that the use of general spin orbitals is essential for the treatment of the spin degeneracy in many-electron atoms. The energy obtained is -7.447536 a.u., which is lower than perviously published values obtained from $s$ orbitals only. The value for the Fermi contact term is $2.846 {{a}_{0}}^{\ensuremath{-}3}$, which is 97.9% of the experimental one. A natural spin-orbital analysis of the wave function is performed.