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 favours the ``inverted-umbrells'' environment seen in real Boron. 
W.-J. Zhu (IBM Yorktown) and C. L. Henley (Cornell U.)