Journal of Physical Chemistry A, Vol.111, No.44, 11294-11301, 2007
Anatomy of bond formation. domain-averaged fermi holes as a tool for the study of the nature of the chemical bonding in Li-2, Li-4, and F-2
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 Li-4 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 Li-2 molecule, which also features such a non-nuclear attractor for a significant range of nuclear separations. Full-Cl wave functions for H-2, 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 H-2 and Li-4, 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 F-2, 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 H-2.