CONTRIBUTION OF DYNAMIC POLARIZATION TO THE BINDING-ENERGIES OF COVALENT BONDS

The valence CASSCF function defines an optimized set of valence orbitals. All the valence-bond (VB) components of this wave function are described using this unique set. The dynamical polarization is brought by the single excitations on all the valence components of the valence CAS. It introduces a relaxation of the orbitals in each VB form. From analysis of the dynamical polarization contributions in H-2, F2 X1SIGMA(g)+ ground state, F2 C1SIGMA(u)- excited state, F2- 2SIGMA(u)+ ground state, and the N-H bond dissociation energy in NH3, we show that the dynamical polarization (which vanishes at the broken bond limit except for the spin polarization) is the leading dynamical binding effect. However, it gives an overestimated value of D(e) for F2 and F2-, leading to the conclusion that the overall contribution of double excitations on the valence space is repulsive in these cases.