Pd_nAl^(±)(n=1—8)二元团簇的密度泛函理论研究

A density functional theory study of small bimetallic Pd_nAl^(±)(n = 1—8) clusters

采用密度泛函理论(DFT)方法,在BPW91/LANL2DZ水平下详细研究了PdnAl±(n=1—8)团簇的几何结构、稳定性和电极化率,并与Pdn+1和PdnAl(n=1—8)团簇进行了比较.结果表明:除n=6,8外,PdnAl团簇和Pdn+1团簇的基态结构保持了相同的构型,除Pd2Al±和Pd6Al+外,PdnAl±团簇的基态结构与PdnAl团簇的保持了相同的结构.且在PdnAl和PdnAl±团簇基态结构中,Al原子位于较高的配位点上.分裂能和二阶能量差分的分析结果表明Pd4,Pd3Al和Pd3Al±团簇相对其他团簇具有较高的稳定性.极化率的研究表明富Pd团簇的非线性光学效应强,容易被外场极化.Pd6,Pd5Al和Pd3Al±团簇的极化率各向异性不变量为最小值,说明相应团簇对外场的各向异性响应最弱,各方向的极化率大小变化不大.

Geometries, stabilities, and polarizations of PdnAl±（n = 1—8） have been calculated using the density functional theory at BPW91/LANL2DZ level. The growth pattern for different sized PdnAl（n = 1—8）clusters is of Al-substituted Pdn＋1clusters, which shows the similar configuration of most stable Pdn＋1clusters except that of Pd6Al and Pd8Al.Geometries of ground state PdnAl±（n = 1—8） clusters keep the same structures of PdnAl clusters except that of Pd2Al±andPd6Al＋. AlatomsinthegroundstatePdnAlandPdnAl±isomerstendtooccupythemosthighlycoordinated position. Analysis of stabilities shows that Pd4, Pd3Al and Pd3Al±are more stable than other clusters. Study of polarizations shows that Pd-rich clusters have a strong nonlinear optical effect and are easy to be polarized by external electromagnetic field.