Crystalline phases of thiourea. I. Model of incommensurate phases

Abstract
A one-dimensional model describing the successive phases in completely deuterated thiourea [SC(ND2)2] is proposed. The stable phases of the model are investigated by numerical and analytical methods. Lock-in phases with wave-vector modulations 17, 18, and 19 have been found. The essential couplings between harmonics of different symmetries have been established.