铜银纳米合金团簇结构转变的原子模拟

Atomic simulation on structural transformation of Cu-Ag nanoalloy clusters

采用基于嵌入原子方法势的分子动力学方法对熔融Cu_(n)Ag_(53-n)(n=0~53)和Cu_(n)Ag_(54-n)(n=0~54)合金团簇的降温凝结过程进行模拟.通过结构相图、自由能、原子化能、形状因子、对分布函数、熵和直观可视化的原子堆积结构等多种计算分析手段,在原子尺度上探究温度、组分和初始构型等对小尺寸Cu-Ag合金团簇在降温凝结中的结构转变以及热力学量的影响.模拟结果表明,在室温下含有少量Cu原子的二元合金团簇可以形成的核壳式二十面体几何结构,同时Cu原子取代Ag原子也有助于合金团簇的稳定.组分的改变和温度的降低使堆积结构由无序变为有序,同时伴随着原子势能、形状因子、熵的振荡下降,低温阶段熵值下降明显.

Molecular dynamics method based on embedded atom method potential has been used to simulate the condensation process of molten Cu_(n)Ag_(53-n)(n=0~53)and Cu_(n)Ag_(54-n)(n=0~54)alloy clusters.The effects of temperature,composition and initial configuration on the structural transformation and thermodynamic quantities of Cu-Ag alloy clusters with small size during condensation at atomic scale were investigated by means of structural phase diagram,free energy,atomization energy,shape factor,pair distribution function,entropy and visualized atomic stacking structure.The simulation results show that core-shell icosahedral geometry can be formed in binary alloy clusters containing a small number of Cu atoms at room temperature,and the substitution of Cu atoms for Ag atoms also contributes to the stability of alloy clusters.The change of components and the decrease of temperature make the packing structure change from disorder to order,accompanied by the decreases of oscillations in atomic potential energy,shape factor,and entropy,and the entropy decreases obviously in the low temperature stage.