Spin-Extended Wave Function for Atomic Sodium

Abstract

The spin-extended Hartree-Fock (SEHF) function, obtained by projecting the appropriate spin component of a UHF determinant with subsequent optimization, is calculated for $\mathrm{Na}\left({}_{}{}^2{}_{}{}^{}S\right)$ with four different basis sets. Energy reductions relative to RHF values are small. Spin density at the nucleus is 12% off experimental value and rather insensitive to changes in basis set. It is tentatively concluded that SEHF spin density values are much more reliable for atoms with open $s$ shells than for those having open $p$ shells.