NONMONOTONICITY OF THE ATOMIC ELECTRON MOMENTUM DENSITY

The observed nonmonotonic behavior of the atomic electron momentum density of neon and some members of its isoelectronic sequence at the Hartree-Fock level is investigated. Further evidence is provided by showing that the nonmonotonicity observed for the neon series at the Hartree-Fock level is still present when a cusp condition and the correct asymptotic behavior are imposed onto the Hartree-Fock wave function. This result is also observed for the results obtained from highly correlated configuration-interaction wave functions. Furthermore, we substantiate the argument that the observed nommonotonicities are most probably due to higher-order terms in the Z-1 perturbation theory.