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 th at every atom is equivalent. Fitting to each subset with a particular Z, we extract a classical effective potential, written as a sum over coordinatio n shells and dominated by three-atom (bond angle dependent) terms. In the c ase 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'' enviro nment seen in real boron.