An effective Hamiltonian was derived, for centers with multi-well potentials, which took account of spatial symmetry, of symmetry with respect to time reversal, and of the Hermitian nature of the initial interaction energy operators. The physical significance of additional terms in the Hamiltonian was examined, their magnitudes were estimated, and their possible effects were pointed out.

A.B.Roitsin: Fizika Tverdogo Tela, 1995, 37[6], 1594-602 (Physics of the Solid State, 1995, 37[6], 865-9)