Study Of The Melting Properties Of Co-Cu Bimetallic Clusters By Using The Gupta Potential Combined With Molecular Dynamics Simulation

Clusters are aggregates of atoms or molecules in nano-scale size, containing a number of constituent particles ranging from 10 to 10⁷. Studying of clusters has been an active field because of their unique structural and physical properties. Many investigations have been done in studying cluster properties both experimentally and theoretically. For the importance in magnetism and catalytic activity, clusters of Co and Cu have attracted considerable attention by many academicians. But to our knowledge, no results have been reported systematically about the geometrical and melting properties of the mixed Co_nCu_13-n (n = 0 13) clusters and the melting behaviors of the mixed Co_nCu_55-n (n = 0 55) clusters.In this paper, we use Gupta potential and the genetic algorithm combining with the molecular dynamics simulations to study the static and dynamic properties of the mixed Co-Cu clusters. Our works contain two parts as follows: (1)The geometrical and melting behaviors of the mixed Co_nCu_13-n (n = 0 13) clusters. (2)The melting properties of the mixed Co_nCu_55-n (n = 0 55) clusters. We summarize our main conclusions as follows:1. The ground-state geometries of all these bimetallic Co_nCu_13-n (n = 1 12) clusters are similar to that of the pure Co₁₃ (Cu₁₃) cluster, and the central site is prefer to surface ones for replacing the Co atom(s) of the Co_nCu_13-n (n=1～12) clusters as comparing that of the Cu₁₃, and the surface Co atoms coalesce together. From analyzing the second-order difference energy and the mixing energy, Co₁Cu₁₂ and Co₇Cu₆ are found to have relatively high stability and can be considered as the magic number clusters; The melting points of Co_nCu_13-n (n=0～12) clusters increase in general with only one abnormal decline at n=3, which can be attributed to that the energy gap between the ground state and the first excited state of Co₃Cu₁₀ cluster is substantially smaller than that of Co₂Cu₁₁ cluster. 2. The absolute value of the average binding energy per atom of the mixed Co_nCu_55-n (n = 0 55) clusters increases with increasing the number of Co atoms, and a jump occurs at the temperature range from solid-like to liquid-like. The melting point of the mixed Co_nCu_55-n (n = 0 55) clusters increases in general with increasing the number of Co atoms,but minor oscillations exist in details, and the melting points of the mixed clusters all locate in the medium of the pure Cu₅₅ and Co₅₅ clusters and are all less than the melting points of the Cu and Co crystals. The variations of the pre-melting intervals of the mixed Co_nCu_55-n (n = 0 55) clusters become larger with small or large Co (Cu) component.