GENERALIZED FRENKEL-KONTOROVA MODEL - A DIATOMIC CHAIN IN A SINUSOIDAL POTENTIAL

To understand modulated structures and commensurate-incommensurate tra nsitions, we generalize the Frenkel-Kontorova model to a diatomic chai n in the presence of an external sinusoidal potential. For the classic al ground states, the diatomic effects are reflected by the phase diag ram and the phonon spectrum. For the quantum ground states, the diatom ic effects are reflected by the distribution of atoms on the external potential, the phase diagram, correspondences between the ground state s and the orbits of the area-preserving maps, the phonon spectrum, and the occurrence of a second critical point K-c' besides K-c at which a transition by breaking analyticity occurs. [S0163-1829(98)06325-5].