Ground State Structure And Physical Properties Of Metal Clusters By Molecular Dynamics Simulation

The geometric structures and energies of Morse clusters and Binary LennardJones clusters have been studied systematically by combining the empirical potentials with different algorithms. This paper includes the following two parts:( 1) The ground-state geometries and energies of the Morse clusters Mn(n=2~100) are systematically studied by the micro-canonic molecular dynamics simulated quenching method based on the Morse-type two-body inter-atomic potential. The calculated results reproduce precisely all the lowest energies of the Mn(n=2~80) clusters listed in the Cambridge Cluster Database, suggesting the efficiency of the micro-canonic molecular dynamics simulated quenching method in searching the ground-state geometries of clusters. The ground-state geometric structures of the Morse clusters Mn(n=2~100) are all icosahedral-like close-packing structures, and generally the average binding energies of those Morse clusters increase with increasing the cluster size. Through analyzing the second- and first-order energy differences, the magic-number sequences of the ground-state Mn(n=2~100) clusters are obtained as n=13,19,23,26,29,36,39,46,49,55,71,83,and 71. With analyzing the average nearest-neighbor distances and the average coordination numbers in further, one can find that the influence of the average coordination number on the stabilities of the ground-state geometries is important, and the influence of the average nearest-neighbor distance can be neglected.(2)The lowest-state geometries and energies of the BLJn(n=5~60) clusters are studied by combining the Lennard-Jones two-body inter-atomic potential with the genetic algorithm. The calculated results reproduce precisely all the lowest-state energies of the BLJn(n=5~60) clusters listed in the Cambridge Cluster Database. Through analyzing the results one can find that: The lowest-state geometries of the BLJ clusters are different from that of the single-element LJ clusters. For example, for the 45-atom size the ground-state geometry of the LJ cluster is not a Ih structure, while that of the BLJ cluster is a perfect Ih one. Through analyzing the connection between the lowest-state geometries and the atomic components of the BLJ clusters, A-class atoms are always grouped together and most of them stand within clusters. It indicates that atoms with smaller radius tend to gather together and most of them stand within clusters when the atomic cohesive energies are equal. And in the lowest-energy geometries of the BLJ clusters, A-class atoms always tend to form a structure with high symmetry. We suppose that the stability of the geometric structures of the BLJ clusters depends on the stability of the geometrical structures formed by A-class atoms strongly. Through analyzing the second-order energy differences of the lowestenergy BLJ clusters with different sizes and the relation between the lowest energy and its closest energy, it’s easy to draw a conclusion that: The larger the energy difference between the lowest-energy state and the nearest-energy state is, the higher the stability of the lowest-energy state holds, and the peak values in the energydifference chart are corresponding to the magic numbers of the BLJ clusters.