Localized modes in monoatomic and diatomic chains due to the anharmonicity

Intrinsic localized modes due to the anharmonicty are discussed in detail in the case of monoatomic chains considering a finite (even or odd) number of particles interacting with nearest neighbours harmonic and quartic anharmonic force constants. We find odd parity and even parity localized modes above the maximum harmonic frequency in the monoatomic case. These modes persist modifying the anharmonic force constant at the center of the chain, but their envelope shape becomes double peaked. Preliminary resylts for diatomic chains are also presented. In tis case we find odd localized modes above the maximum harmonic frequency and in the gap between the acoustic and optic continuum.