Relaxation modes for trapped crystal point defects

Group representation theory is applied to the problem of calculating the relaxation modes of a point defect trapped near an impurity atom or other defect in a crystal, where more than one set of neighboring sites is available to the point defect. For illustration, the case of a cation vacancy trapped near a divalent impurity in the sodium chloride lattice is treated, including nearest- and next-nearest-neighbor sites.