ELECTRON MOMENTUM DENSITIES OF ATOMS

Spherically averaged electron momentum densities Pi(p) are constructed by the numerical Hartree-Fock method for all 103 atoms from hydrogen (atomic number Z = 1) to lawrencium (Z = 103) in their experimental gr ound states, We find three different types of momentum densities sprea d across the periodic table in a very simple manner for the 98 atoms o ther than He, N, Mn, Ge, and Pd. Atoms in groups 1-6, 13, and 14, and all lanthanides and actinides have a unimodal momentum density with a maximum at p = 0, atoms in groups 15-18 have a unimodal momentum densi ty with a local minimum at p = 0 and a maximum at p > 0, and atoms in groups 7-12 have a bimodal momentum density with a primary maximum at p = 0 and a small secondary maximum at p > 0. Our. results confirm the existence of nonmonotonic momentum densities reported in the literatu re, but also reveal some errors in the previous classification of atom ic momentum densities. The:physical origin for the appearance of the t hree different modalities in Pi(p) is clarified by analysis of subshel l contributions to momentum densities. (C) 1998 American Institute of Physics.