VALENCE SHELL STRUCTURES IN THE DISTRIBUTIONS OF THE LAPLACIAN OF THEELECTRON-DENSITY AND THE ONE-ELECTRON POTENTIAL FOR DIATOMIC-MOLECULES

The-valence shell charge concentration, VSCC, in an atom is defined by Bader as the outermost spherical region for which del(2) rho(r)<0. We compare and contrast an alternate definition of the VSCC as the outer most spherical region for which del(2) root rho(r)/2 root rho(r)<0. Th e quantity del(2) root(r)/2 root rho(r), termed the one-electron poten tial (OEP), is implicit in the (exact) one-electron Schrodinger equati on. In a homonuclear diatomic bound by shared interaction, the VSCCs o f the atoms are merged. Provided that the merged VSCCs persist, the di atomic is enclosed by an outermost zero-valued surface encompassing th e VSCC of the molecule. The outermost del(2) rho(r)=0 surface is terme d the reactive surface while the outermost OEP=0 surface is termed the molecular envelope. In cases where the VSCCs are not revealed in the atoms, the reactive surfaces and molecular envelopes are incomplete or absent in the diatomics. We show that in many diatomics the molecular envelope is present although the reactive surface is missing. In an i onic diatomic bound by closed-shell interaction, the VSCC of the catio n can disappear. Otherwise, fragments of the cationic VSCC, termed lig and-opposed charge-concentration (LOCC), may remain opposite to the an ion. In general, the LOCC is absent when the VSCC is not revealed in t he atom. We show that the LOCC is more widespread in the distribution of OEP than del(2) rho(r). (C) 1998 American Institute of Physics.