高压固氩晶体构型与材料属性的研究

Investigations of crystal configuration and material properties of high-compressed solid argon

为研究面心立方结构(fcc)固氩的高压压缩特性和热力学特性,本文运用超分子单、双(三)重激发耦合簇理论(CCSD(T))ab initio法计算原子间距在2.0~3.3A下室温fcc固氩的多体相互作用势,得到固氩两体、三体和四体势团簇的构型以及两体和三体势的截断位置、收敛性、多体结合能和高压压缩特性,并与前期理论计算结果、实验值进行比较。结果表明:(Ar)2团簇的总原子数是903,属于12种不同的几何构型,(Ar)3是861,属于25种不同的几何构型,(Ar)4是816,属于28种不同的几何构型;仅考虑两体、三体项,且近邻原子数为42时,总多体势能Un在原子间距R≥2.3 A时收敛,而当R<2.3 A时,需要考虑四体项或者更多的近邻原子才能收敛;其多体展开式是一交换级数;零点振动能大约为总结合能的6%,已不可忽略。通过比较发现,本文的计算结果和实验数据在80 GPa内完全吻合。

In order to study the high-compressed and thermodynamic properties of face-centered cubic(fcc)solid argon,using full single and double excitations plus perturbative treatment of triples(CCSD(T))ab initio method,we established and discussed the fcc atomic crystal configurations of two-,three-,four-body terms,and multibody potential energy of solid argon.The results show that the total number of(Ar)2 clusters is 903,belonging to 12 different geometric configurations;(Ar)3 is 861,belonging to 25 different geometric configurations,and(Ar)is 816,belonging to 28 different geometric configurations.The total potential energy Un reach saturation when R≥2.3 A and only consider two-,three-body interaction energy with 42 neighbor atoms;when R<2.3 A,it is necessary to consider four-body or more neighbor atoms to converge.Multibody expansion of fcc is an exchange series.The zero-point vibration energy is about 6%of the total cohesive energy,but it should not be neglected.Finally,by comparison,the calculated results are in good agreement with the experimental results within 80 GPa.