Journal of Statistical Physics, Vol. 95, Nos. 56, 1999. p. 1323-1336.
The conventional permutational statistics of cooperative phenomena is extended to include displacement of atoms from their reference lattice points. The formulation is done in the cluster variation method (CVM) framework, by changing summations in energy and entropy to integrals. It is demonstrated for the pair approximation of CVM on phase-separating fee binary alloys. The treatment can take into account local lattice distortion due to atomic size difference, the elastic effects, and the pressure effects.