Discrete breathers in realistic models: hydrocarbon structures

Discrete breathers (DBs), or intrinsic localized modes, are time-periodic spatially localized solutions that exist generically in nonlinear discrete models and persist as long-lived robust solutions when they are not resonant with linear excitations. Without using the powerful but rather technical self-consistent methods of calculation already developed and applied to DBs in relatively simple models, we study DBs with tight-binding molecular dynamics simulations using a realistic model for carbon-hydrogen systems. We focus here on the carbon-hydrogen stretch vibrations, whose frequencies are well separated from the rest of the vibrational modes. We show that in the anharmonic region of the interaction potential these spatially localized solutions persist for time scales which are orders of magnitude longer than the period of the atomic vibrations and with frequencies that are different from the: normal-mode frequencies. The conditions under which these DB solutions are created, the implications on energy relaxation, and experimental evidence of their existence are discussed. (C) 2001 Elsevier Science B.V. All rights reserved.