铝-4d过渡族金属二聚体的第一性原理计算

The First Principle Study of AlX (X=4d elements) Dimer

关键词:  二聚体  第一性原理  过渡族金属铝化物  成键特征

Key words:  dimer  first-principles  transition metal aluminides  bonding characteristic

摘要:

[目的]过渡族金属与铝之间的化学成键特性是化学与材料等领域的基础,对铝-4d过渡族金属二聚体的物理性能进行研究。[方法]用密度泛函B3LYP方法计算铝-4d过渡族金属二聚体的键长、振动频率、解离能、电离势、能隙和二极矩。[结果]对中性和荷电的二聚体,除AlMo、AlNb⁺和AlMo⁺外其键长从AlY到AlPd先减少后增加,解离能和振动频率的变化趋势与之相反。电离势随原子序数的递增先增加,在AlRh处达到极大值后减少。除AlTc的振动频率外,计算结果与已有的实验结果和其他的理论计算结果相符。计算结果还显示除AlCd外,前过渡族金属与铝的结合强度比后过渡族金属的结合要强。荷电二聚体的自旋多重度比相应的中性二聚体差±1。带正电的二聚体的键长比中性和带负电的二聚体的键长要长,荷电二聚体的解离能大于中性二聚体的解离能,解离方式为AlX⁺→X+Al⁺和AlX^-→Al+X^-。

Abstract:

[Objective] The nature of chemical bond between a transition metal and aluminium is a base of chemistry and materials science. The physical properties of AlX (X=4d elements) Dimer were studied.[Methods] Bond length, vibrational frequency, dissociation energy, ionization potential, energy gap and dipole moment of the title molecules in neutral and charged ions were studied by density functional method B3LYP.[Results] For neutral and charged molecules, the bond length decreases from AlY (AlY⁺ and AlY^-) to AlPd (AlPd⁺ and AlPd^-) except AlMo, AlNb⁺ and AlMo⁺, and then increases.Opposite trends are observed for dissociation energy and vibrational frequency.The ionization energy through the series increases and reaches the maximum at AlRh and then decreases.The present results are in good agreement with the available experimental and other theoretical values except the vibrational frequency of AlTc.The present calculations show that the late transition metal can combine strongly with aluminum compared with the former transition metal (except AlCd).For cationic dimer, the dissociation procedure of channel AlX⁺→X + Al⁺ is easier than that of channel AlX⁺→Al + X⁺.However, for anionic dimer, the channel AlX^-→Al + X^- is favorable except AlY^-, AlPd^- and AlCd^-.The ground state spin multiplicity of the charged ions differs by ±1 from that of the corresponding neutral parent.The bond length of AlX⁺ is larger than that of AlX (except AlPd) and that of AlX^- (except AlRu^- and AlPd^-).The dissociation energy of charged dimer is bigger than that of neutral counterpart.