Anatomy of Bond Formation. Domain-Averaged Fermi Holes as a Tool for the Study of the Nature of the Chemical Bonding in Li2, Li4, and F2

Abstract

Domain-averaged Fermi hole (DAFH) analysis represents a relatively new strategy for extracting useful new insights into electronic structure and bonding from correlated wave functions. We analyze a full-valence CASSCF description of the Li4 rhombus, in order to discern the role played by the domains of the non-nuclear attractors in the sharing of the valence electrons. Similarly we examine the electron reorganization that accompanies the bond dissociation process in the Li2 molecule, which also features such a non-nuclear attractor for a significant range of nuclear separations. Full-CI wave functions for H2, for a wide range of bond lengths, are used to determine how robust are the DAFH descriptions from full-valence CASSCF wave functions to the incorporation of dynamical electron correlation. Comparisons are made, for H2 and Li4, with a much cheaper strategy in which restricted Kohn-Sham orbitals from B3LYP calculations are inserted into a simplified DAFH expression which applies at the restricted Hartree-Fock level. We also investigate the breaking of the relatively weak F-F bond in F2, in order to determine the extent to which the DAFH analysis of such a system differs from that of a more conventional homopolar bond, such as the one in H2.