Electron momentum densities of atoms

Abstract

Spherically averaged electron momentum densities Π(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 ground states. We find three different types of momentum densities spread across the periodic table in a very simple manner for the 98 atoms other 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 density 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 literature, but also reveal some errors in the previous classification of atomic momentum densities. The physical origin for the appearance of the three different modalities in Π(p) is clarified by analysis of subshell contributions to momentum densities.