A new compressible ion model for describing the energetic components of the
cohesive energy of a fully ionic crystal is developed and tested using pre
vious ab initio results for three cubic phases of MgO. This model is physic
ally highly transparent and improves on previous compressible ion models in
two ways. First, the short-range cation-anion interaction and the rearrang
ement energy needed to convert a free O- ion plus a free electron into an O
-2 ion having a form optimal for its in-crystal environment are decomposed
into the major contributions originating from the six outermost anion elect
rons plus smaller terms generated by the two 2s electrons. This model trans
fers to the B2 and B3 phases of MgO after parametrization on the ab initio
data for the B1 phase even more accurately than previous compressible ion m
odels. Second, the separate modeling of the repulsive (permutation) and att
ractive (penetration) components of the short-range anion-anion interaction
s enables the new model to describe their subtle dependencies on the in-cry
stal anion environment that lie beyond the scope of previous models. The ne
w model is also used to illuminate the behavior of two fluorite oxides. (C)
2001 American Institute of Physics.