液态金属凝固过程原子团簇结构表征的新方法（英文）

采用分子动力学方法对液态金属钠的凝固过程进行了模拟计算,运用团簇结构表征新方法――团簇类型指数法(CTIM)对凝固过程中的团簇结构进行了识别.为了阐明CTIM在识别团簇结构上的准确性和效率,将其与广为采用的Voronoi多面体方法 (VPM)进行比较.结果表明:当采用CTIM和VPM分别对液态金属钠凝固结构中的原子团簇结构进行表征时,它们所得到的微观结构特征是一致的.非晶态结构中,原子团簇类型的分布呈现明显的区段特征,每一区段都存在一种主要团簇类型,它们分别是二十面体或其缺陷结构.晶体结构中,体系形成以BCC团簇为主体的晶态结构.同时发现,VPM不易区分不同团簇构型之间的细微差别,不同构型的原子团簇可能被归为同种结构类型;而CTIM根据近邻原子之间相对位置关系,直接准确描述原子团簇的构型.不但由CTIM分析获得的凝固体系结构特征与VPM的分析结果一致;而且CTIM抓住了体系微观结构特征的主要方面,简化了团簇结构的表征形式,这在大尺度模拟体系的结构分析中将具有较高效率.

A new method for structural characterization of atomic clusters in solidification processes of liquid metals*

A molecular dynamics simulation has been performed on the solidification process of liquid Na, and the atomic clusters in the solidification process have been identified by means of a new characterization method -- cluster-type index method (CTIM) proposed by us. In order to evaluate the reliability and efficiency of CTIM, it is compared with the widely used Voronoi polyhedron method (VPM). Our results show that when the atomic clusters in the solidification structures of liquid Na are characterized by the VPM and CTIM, respectively, their structural features are identical. The distributions of atomic clusters in the amorphous structure characterized by the two different methods both display several broad peaks, and each peak corresponds to one favorable cluster type. The favorable cluster types both are icosahedron and its defective cases. The dominated cluster type in the crystal structure characterized by the two different methods both is bcc crystal unit. It is also found that the VPM is difficult to distinguish the small differences between cluster configurations according to the shapes of Voronoi polyhedra, and different cluster configurations may be classified into the same type. The CTIM directly describes cluster configurations according to the position relations of neighbor atoms. CTIM simplifies the representation format of atomic clusters by means of outstanding the principal ones. This will be efficient in the structural analysis of larger-scale simulation systems.