EFFECT OF DISCRETE BREATHER ENSEMBLES ON THE HEAT CAPACITY OF NONLINEAR CHAINS

10.25712/ASTU.1811-1416.2023.04.001

Abstract

A discrete breather (DB) is a spatially localized and time-periodic high-amplitude oscillatory mode in a nonlinear lattice. Experimental and molecular dynamics studies have confirmed that DBs can be excited in various crystal lattices, and when interacting with point defects, they can reduce the potential barrier to their migration. This, in turn, can affect the structure of the crystal and its properties. In this paper, we model a nonlinear one-dimensional crystal with particles whose interaction is described by a linear interparticle and a nonlinear on-site potential. DBs were introduced into a crystal with a hard or soft type of nonlinearity in an amount from 1 to 7 and with an oscillation amplitude from 0.5 to 3. It was found that the number of DBs in the ensemble does not affect the change in heat capacity, but heat capacity depends on the DB oscillation amplitude. In the case of a soft type of nonlinearity, the heat capacity increases with an increase in the oscillation amplitude, and in the case of a hard type of nonlinearity, an inverse relationship is observed. The effect on the heat capacity of an ensemble consisting of DBs with different oscillation amplitudes was also studied. An expression is obtained for determining the heat capacity in such cases. This work shows that the presence of DBs in crystals can be judged from their effect on the heat capacity. To achieve this goal, it is necessary to calculate the DB concentration in the crystal as a function of temperature. The development of methods for indirect confirmation of the existence of DBs in crystals is an important task due to the lack of methods for their direct observation to date.