Subshell momentum splitting and double-zeta description of many-electron atoms

When two subshell electrons are considered simultaneously in many-electron atoms, the average subshell momentum (p)nl splits into two different momenta, low momentum (p<)nl and high momentum (p>)nl, where n and l are the principal and azimuthal quantum numbers. For the 102 atoms He through Lr in their ground states, the momenta (p<)nl and (p>)nl, as well as the momentum separation (|p1 - p2|)nl, are systematically examined at the Hartree-Fock limit level. For a subshell nl, two exponents ζnl<(est) and ζnl>(est) estimated from the low and high momenta have good linear correlations with variationally determined exponents ζnl<(var) and ζnl>(var) used in the double-zeta description of atoms with Slater-type basis functions