INFLUENCE OF LINEAR DISCRETE BREATHERS ON MACROSCOPIC PROPERTIES OF FCC CRYSTALS

10.25712/ASTU.1811-1416.2024.04.004

Abstract

The effect of a one-dimensional nonlinear vibrational mode on the macroscopic properties of defect-free fcc crystals (Al, Cu, and Ni) was studied using the molecular dynamics method. Standard potentials based on the embedded atom method were used to describe the interaction between atoms. In a three-dimensional computational cell, a nonlinear vibrational mode is excited by moving even and odd atoms in opposite directions of the atomic chain along the close-packed crystallographic direction [10-1]. The amplitudes of the initial atomic displacements varied within 0.05-0.5 Å. The amplitudes of atoms decrease  exponentially with increasing distance from the excited atomic chain. The obtained vibrational modes in Al, Cu, and Ni have a hard type of nonlinearity, i.e. their frequency increases with increasing amplitude. The mode is capable of accumulating vibrational energy in the range from 0.9 to 3.4 eV per atom. The heat capacity or the ability to store energy of the system decreases for fcc metals with increasing amplitude. Excitation of a one-dimensional nonlinear vibrational mode leads to the appearance of compressive stresses, which corresponds to the thermal expansion of the crystal. Due to the high degree of spatial localization along one direction, the considered one-dimensional vibrational mode can be considered as a linear discrete breather. Calculations performed for a Ni single crystal with two different computational cells showed that a change in size does not affect the characteristics of a linear discrete breather.