采用密度泛函理论对二元合金PbnAgn (n=2-12)团簇的结构和电子性质进行研究

摘要

Structural and electronic properties of PbnAgn (n=2-12) clusters were investigated by density functional theory with generalized gradient approximation at BLYP level in DMol3 program package.The optimized bimetallic PbnAgn (n=2-12) clusters were viewed as the initial structures,then,those were calculated by ab initio molecular dynamics (AIMD) to search possible global minimum energy structures of PbnAgn clusters,finally,the ground state structures of PbnAgn (n=2-12) clusters were achieved.According to the structural evolution of lowest energy structures,Ag atoms prefer gather in the central sites while Pb atoms prefer external positions in PbnAgn (n=2-12) clusters,which is in excellent agreement with experimental results from literature and the application in metallurgy.The average binding energies,HOMO-LUMO gaps,vertical ionization potentials,vertical electron affinities,chemical hardness η,HOMO orbits,LUMO orbits and density of states of PbnAgn (n=2-12) clusters were calculated.The results indicate that the values of HOMO-LUMO gaps,vertical ionization potentials,vertical electron affinities and chemical hardness η show obvious odd-even oscillations when n≤5,PbnAgn (n=2-12) clusters become less chemically stable and show insulator-to-metal transition with the variation of cluster size n,PbnAgn (n≥9) cluster are good candidates to study the properties of PbAg alloys.Those can be well explained by the density of states (DOS) distributions of Pb atoms and Ag atoms between-0.5 Ha and 0.25 Ha in PbnAgn (n=2-12) clusters.%采用密度泛函理论中的GGA-BLYP近似对PbnAgn (n=2-12)团簇的结构和电子性质进行研究,且所有的计算都是在DMol3模块中进行的.采用优化过的PbnAgn (n=2-12)团簇作为从头算分子动力学的初始结构并采用从头算分子动力学对其基态结构进行搜索,最终得到了PbnAgn (n=2-12)团簇的基态结构.基于PbnAgn (n=2-12)团簇的基态结构演变规律发现,Ag原子倾向于聚集在一起且占据在团簇的中心的位置而被周围的Pb原子包围,这也与铅富集贵金属的现象以及文献报道的实验结果一致.对PbnAgn (n=2-12)团簇的平均结合能、HOMO-LUMO能隙、垂直电子电离势、垂直电子亲和势、化学硬度η、HOMO轨道、LUMO轨道和态密度进行了计算.研究结果表明,当n≤5时,HOMO-LUMO能隙、垂直电子电离势、垂直电子亲和势和化学硬度η的值显示出了明显的奇-偶振荡现象;随着团簇尺寸的增大,PbnAgn (n=2-12)团簇的化学稳定性降低,且显示出由绝缘性向金属性的过渡;PbnAgn(n≥9)团簇是用于计算Pb-Ag合金性质的理想候选者.这些可很好地用铅原子和银原子在-0.5 Ha～0.25Ha之间的态密度(DOS)来解释.