A comparative study on local atomic configurations characterized by cluster-type-index method and Voronoi polyhedron method

To assess strengths and weaknesses of cluster-type-index method (CTIM) and Voronoi polyhedron method (VPM) in the characterization of local structures, the similarity and difference between CTIM clusters and Voronoi polyhedrons (VPs) in under-cooled liquids and rapidly solidified solids of silvers are analyzed from the configurational view of point. By tracking identification numbers of atoms, it is found that one kind of VPs usually corresponds to several kinds of CTIM clusters with same or higher coordination number of central atoms, and the local structures of fcc lattices and hcp lattices can hardly be distinguished from each other merely based on their Voronoi polyhedron indexes 〈0, 12, 0, 0〉. In CTIM, the fcc and hcp basic clusters can be characterized by (12, 12/1421) and (12, 6/1421, 6/1422), respectively, but their total are less than the population of 〈0, 12, 0, 0〉 VPs in the same simulated system. A careful analysis of VPs with and without refinement reveals that the diminishment of shell atoms associated with tiny Voronoi polygons should be responsible for low coordination numbers of central atoms in VPs relative to their counterparts of CTIM clusters. The CTIM based on Honeycutt-Andersen (H-A) pair analysis can identify more kinds of atomic clusters, but its multi-indexes nature makes the feature extraction from various local atomic configurations more difficult.