Use of CI Methods for the Study of Molecular Dissociation Processes in Various Electronic States

Abstract

The adequate description of bond-breaking processes is a difficult problem since it requires very good correlated wavefunctions to account for the generally quite large difference in correlation energy between the combined system and the individual fragments. The situation is especially critical if multiple bonds are broken as in N₂, for example, for which the single-configuration Hartree-Fock treatment yields only a dissociation energy of D_e= 5.18 eV [1], i.e 4.72 eV below the experimental result [2]. But even in systems containing only a single bond such as F₂ the use of correlated wavefunctions is essential since it is well-known that this molecule is not even found to be bound with respect to two F atoms in the Hartree-Fock approximation. And finally it is also obvious that extremely weak bonds like van der Waals interactions can only be described by methods going beyond the single-configuration approach.