Surface and gap intrinsic localized modes in one-dimensional lattices

In this paper we discuss the intrinsic localized modes of diatomic anharmonic chains for two different geometries, which simulate a row of a zinc-blende three-dimensional crystal or a row of an alkali-halide crystal. The modes are determined with two different potential models, using the full potential or the Taylor expansion truncated to fourth order. We obtain bulk modes and two kind of surface modes in the frequency gap between acoustical and optical phonons.