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Nonclassical origin of the rocksalt-cesium chloride structural transition.

One of the outstanding problems in crystal physics is the role nonclassical forces play in stabilizing the cesium chloride versus rocksalt structure for ionic solids. By consideration of classical electrostatic and repulsive forces alone, it is not possible to predict accurately which structure is more stable. I demonstrate on the basis of ab initio pseudopotential calculations that the cesium chloride structure is not stabilized solely on the basis of charge-transfer effects, or size effects. Rather, nonclassical (s-p nonlocal) effects appear to be crucial in stabilizing the cesium chloride structure.