Effective potentials for 6-coordinated boron: Structural geometry approach

We have built a database of ab initio total energies for elemental boron in over 60 hypothetical crystal structures of varying coordination Z, such that every atom is equivalent. Fitting to each subset with a particular Z, we extract a classical effective potential, written as a sum over coordination shells and dominated by three-atom (bond angle dependent) terms. In the case Z = 6 (lowest in energy and most relevant), the classical potential has a typical error of 0.1 eV/atom, and favors the "inverted-umbrella'' environment seen in real boron.