High-amplitude oscillations of an atomic row in a model crystal

Abstract

Localized excitations in discrete systems have a significant effect on their properties. At the same time, the conditions for the existence of such objects as discrete breathers, quasi-breathers, solitons can be very specific. In this paper, the behavior of atomic rows of various lengths that perform harmonic oscillations is considered using the molecular dynamics method. A crystal of stoichiometry A3B is considered, in which the existence of discrete breathers is possible due to the presence of a forbidden zone in the phonon spectrum. The model was a crystal with a linear size from 5 to 75 unit cells. All atoms of the chain at the initial moment of time were disturbed from equilibrium by a value from 0.2 Å to 0.9 Å. The number of formed discrete breathers was calculated directly from the data obtained in the calculations, i.e. the frequency and amplitude of each atom of the chain were calculated, only oscillations with amplitudes above 0.3 Å were recognized as breathers. The dependences of the number of discrete breathers on the length of the initial chain of atoms and the magnitude of the initial disturbances were obtained.