WHAT IS THE BOND IN BOND VALENCE? USING QUANTUM CHEMISTRY TO BENCHMARK BOND-VALENCE THEORY

The bond-valence model (BVM) has long been very useful for determining the plausibility of proposed equilibrium structures, but a number of attempts are now being made to use BVM-based structural descriptors within atomistic potential energy models. To make such models as useful as possible, we need accurate functions describing bond valence over a wide range of conditions outside of those found in equilibrium structures. In this research, we use AIM theory (Bader’s Atoms In Molecules) coupled with high quality quantum mechanical calculations to examine the mathematical form of bond-valence-bond-length correlations. There are many mathematical similarities in the description of bonding in these two theories: both contain, for example, a monotonically decreasing, bond strength with distance, and both consider the geometry to directly give us the bonding, and therefore the chemistry. The differences are also suggestive of the limitation of the first generation implementation of bond-valence theory. To demonstrate these points, we examined the complete set of Hetero- and Homo- diatomic molecules from H to F (not He), comparing the bond density at the critical points to the description of bond-valence theory.