Topographical view of molecular electron-momentum densities

Abstract

Topographies of ground-state electron-momentum densities (EMD's), γ(p), are studied for a number of diatomic as well as polyatomic molecules and compared with the corresponding separated atom-momentum densities with a view to bring out clearly the effect of bonding from a momentum-space standpoint. All possible critical points of rank three are seen to occur in the molecular EMD topology. Some linear molecules, in particular, are seen to possess a ring of stable critical points. Diatomic molecules constituted of atoms with exclusively s-type orbitals exhibit, in their γ(p) topography, a maximum at p=0. Whenever for any di- or polyatomic system γ(0) is maximal, it turns out to be a unique critical point, whereas for all other cases of criticality at p=0 a definite hierarchy, dictated solely by the criticality at the origin, in the nature of critical points elsewhere is observed. Criticality at p=0, while being imperative, is seen to have a direct bearing on the anisotropies in EMD that manifestly are chiefly characteristic of molecular, rather than separated-atom, EMD. Further, from studies carried out on some isoelectronic series of diversified polyatomic systems, a correlation between the curvatures associated with the p=0 criticality and distribution polarity is discovered.