Collective oscillations of systems of Xe atoms in a groove between two carbon nanotubes

Abstract

The collective oscillations of systems of Xe atoms adsorbed in a groove between two carbon nanotubes have been studied by the method of molecular dynamics. The one-dimensional and three-chain structures of atoms that appear in such grooves are considered depending on the number of particles, temperature, and external potentials. It is shown that the infinite one-dimensional structures of Xe atoms are stable at finite temperatures only in the presence of such potentials acting in the direction normal to the axis of the structure. The oscillation spectrum is found, which is in accordance with theoretical calculations of the dispersion laws of collective modes. Collective oscillations of three-chain structures have been studied. The theoretical calculation of the laws of dispersion of modes, carried out by the method of equations of motion for small displacements of atoms from the equilibrium position, showed that the collective modes of the system show a great similarity with the corresponding dispersion laws of a one-dimensional chain of atoms. At the same time, it was found that a torsion mode arises, which is characteristic of a three-chain structure. The calculation agrees well with the spectrum of oscillations obtained by the molecular dynamics method. Using the established mode dispersion, the heat capacity of Xe chains is calculated within the framework of the Einstein model. The calculation results are in good agreement with the experimental data in the temperature range of up to 35–40 K, which can be explained if we assume the presence of both one-dimensional and three-chain structures of Xe atoms adsorbed in the grooves between carbon nanotubes. The effect of temperature on the stability of Xe atomic structures on nanotubes has been studied, and it has been shown that one-dimensional structures start to defragment at temperatures higher than 60 K, whereas three-chain structures defragment at temperatures higher than 90 K.