Voronoi Polyhedron Investigation of the Short-Range Order in Liquid Bismuth Using Molecular Dynamics Simulation Data

Liquid bismuth is an actual object for research due to the specific features experimentally detected on the temperature dependences of a number of properties, the nature of which is still debatable. Earlier, we used ab initio molecular dynamics simulation to calculate the temperature dependences of a number of properties of liquid bismuth, which demonstrated nonmonotonic behavior. The atomic coordinates determined by molecular dynamics simulation are used in this work for a further investigation of the structural features by the Voronoi polyhedron (VP) method. VPs are constructed in such a way that they fill the space inside a disordered structure without gaps and overlaps and are fundamental geometric figures, which allow us to analyze an atomic structure in terms of precise topological and metric characteristics. The following characteristics are calculated: the distribution over the distances to the nearest neighbors, the distribution over the number of VP faces, the distribution over the number of pentagonal faces, and so on. An analysis of the obtained characteristics of VPs allow us to trace the tendency of changing the structure of the Bi melt at temperatures above the melting point and to reveal deviations from monotonic behavior on the temperature dependences. In particular, the nonmonotonic behavior of the number of polyhedra with pentagonal faces is interesting: it increases sharply at an overheating of about 150 K above the melting point. On the whole, the results point to smooth restructuring of the short-range order in liquid Bi at a small overheating, which is reflected on the temperature dependences of the properties.