Study on two generalized FK models

We study two generalized FK models. Each describes a chain of atoms connect ed by double-well interactions in the presence of a perturbed sinusoidal ex ternal potential. The phase diagram varies with the period of the external potential D and with the amplitude of the perturbation epsilon. Some novel and complex phase structures are found. There are two threshold values of D for each model, which equal the distance and two times of the distance bet ween the two wells of the interatomic interactions, respectively. Within di fferent interval of D, the phase diagrams exhibit different behaviors.