Table : Calculated physical constants for various crystal phases of MgO. The lattice constants a 0 and c 0 are given in Å and bulk moduli B 0 in GPa. The heat of formation ∆ f H and the oxygen vacancy energy E f were calculated using Equations ( ) and ( ) and are given in eV. !"# !$# We incorporated the vacancy energy E v of an oxygen atom in the rocksalt bulk structure with a low weighting in the force field training to use it as a validation measure for the obtained bonding, off-diagonal, and valance parameters. The vacancy energy calculated with the force field equals -6.82 eV and deviates very slightly from the DFT reference (-6.71 eV).