Study On The Structure、Stability And Melting Properties Of Pt And Pd Mixed Clusters

The properties of the clusters are not only different from the individual atoms or molecules, but also different from the macroscopic solid or liquid. Cluster science involves many aspects of chemical and physical problems, and play an important role in the field of catalyst, fuel cell and nano science. In the catalytic field, noble metal catalysts have important status, because nano noble metal catalysts have high catalytic activity,which has great advantages compared with the traditional catalysts. In this paper, two kinds of noble metal Pt and Pd mixed clusters were studied. The structure、 stability and some thermodynamic properties were analyzed.The research methods used in this paper are molecular dynamics. The objects of the study are 12-31 atom PtPd mixed clusters, and the number of Pd atoms in the cluster is 0-8. In this paper, the geometric structure of the mixed clusters is obtained by using the simulated annealing method, and the stability of the mixed clusters is analyzed by using the second order difference of the potential energy. At last, the root-mean-squared pair separation fluctuation of the mixed clusters at different temperatures is calculated, and the melting characteristics of the mixed clusters are analyzed by making δ-temperature T diagrams.After detailed analysis, this paper mainly has the following conclusions:1) The ground state structures of the 13 atom and 19 atom PtPd clusters have high symmetry. Except the 13 atom and the 19 atom mixed clusters, the remaining clusters do not have high symmetry.2) In the scope of this paper, 12-31 atom PtPd mixed clusters were studied. The results show that the mixed clusters can be thought as the evolution of the icosahedron or double icosahedron. Part of the clusters can be observed with regular icosahedral or double icosahedral structure in it.3) The number of Pd atoms in the Pt Pd mixed cluster is not more than 8,and the symmetry of the mixed clusters structure can be enhanced with the increase of the number of Pd atoms in the clusters.4) The stability of the 13 atom clusters is the best.5) The stability of Pt Pd mixed clusters is not only related to the total number of atoms in the clusters, but also related to the proportion of the two kind atoms.6) The pre-melting temperature of the 13 atom clusters is the highest, and the majority of the 19 atom clusters is also higher than others.7) The pre-melting temperature of PtPd mixed clusters is not only related to the total number of atoms in the clusters, but also related to the proportion of the two kind atoms.8) In discussed range of this paper,the pre-melting temperature of half of the common PtPd mixed clusters is very low, most of the rest began pre-melting under 500K9) On the whole,the pre-melting temperature of the PtPd mixed clusters increases with the increase of the number of Pd atoms in the clusters.10) When 14-18 atoms PtPd mixed clusters is melting, two-step melting phenomena can be found obviously.When the number of the atoms in the clusters is more than 19,the two-step melting phenomena is gradually disappear.