SOME 2-ELECTRON PROPERTIES OF SODIUM

Some properties of atoms defined in terms of two-electron operators ar e investigated for sodium. Systematic multiconfiguration Hartree-Fock (MCHF) methods are used. Of particular interest are the energy, the is otope shift parameter, and a dipole-dipole parameter defined as the ex pectation value of the operator (Sigma(i)r(i))(2). Unlike the one-elec tron dipole operator, where the line strength was predicted accurately from single, double, and triple excitations, these properties require that quadruple excitations also be considered.