Effect of molecular dissociation on the exchange-correlation Kohn-Sham potential

The effect of molecular dissociation on the exchange-correlation Kohn-Sham potential vxc has been studied by the construction of vxc from the ab initio correlated density {ρ} for the monohydrides XH (X=Li, B) at several bond distances R(X---H). The molecular dissociation manifests itself in the formation of a characteristic peak of vxc in the bonding region. The partially integrated conditional probability amplitude {Φ}(s₁, x→₂,..., x→N|r→₁) has been used to analyze the behavior of vxc by means of a partitioning into various components: the potential of the exchange-correlation hole vxcʰᵒˡᵉ, the kinetic component vc,kin, and the ``response'' component vᵣₑₛₚ. These components have been constructed from ab initio correlated first- and second-order density matrices. The peak of vxc in the bonding region has been represented as a combination of the corresponding peak of vc,kin and the positive buildup of vᵣₑₛₚ around the more electronegative atom H. Using the conditional amplitude analysis, the asymptotical expressions have been obtained for vᵣₑₛₚ and its positive buildup for the general case of a heteroatomic molecule AB. The dependence of the Kohn-Sham energy characteristics such as the kinetic energy of noninteracting particles Tₛ, the kinetic part of the exchange-correlation energy Tc, and the energy of the highest occupied molecular orbital εN on the bond distance has been studied. The results obtained have been compared with those for the homoatomic two-electron H₂ molecule. {} 1996 The American Physical Society.