THERMAL STABILITY AND MELTING OF THE CORE-SHELL Pd@Pt NANOCUBE: A MOLECULAR DYNAMICS STUDY

Within the framework of the methods of molecular dynamics, simulation of temperature stability of the core-shell Pd@Pt nanocube was performed, and the melting temperature of the sample was determined. During the simulation of the dynamic behavior of the nanocube, the calculation of forces of interatomic interactions was carried out by the embedded atom method. To simulate the melting process, the temperature of the sample was gradually increased by scaling the corresponding atomic velocities using the Berendsen thermostat in the temperature range 300-2500 K. The Lindemann index was used as a numerical parameter describing changes in the structure of a nanoparticle. According to the results of the study, the temperature dependence of the Lindemann index and the average potential energy was obtained, as well as the radial distribution functions for the Pd@Pt nanocube at different temperatures. The obtained dependences have a typical form: they first increase monotonically in the temperature range 300 <= T <= 1700 K, and when the temperature reaches about 1750 K, the Lindemann index and potential energy begin to increase rapidly, which may be considered as the beginning of the melting process. From the simulation results, atomistic configurations of the sample were built, and the dynamics of changes in its structure was investigated. The effect of spatial distribution of atoms on the Lindemann index within the volume of the sample around the melting temperature was also calculated. As it follows from the obtained data, the melting of Pd@Pt nanocube begins in the core of the sample, which consists of Pd atoms. At the same time, the surface of the Pt shell also can be melted partially. The calculated data allowed us to determine the temperature where destruction of the crystalline structure of the sample occurs.