Empty interatomic space in computer models of simple liquids and amorphous solids

Abstract

It is suggested to define the cavities that make up the empty interatomic space of any atomic model as associated overlapping interstitial spheres. The latter are determined unambiguously by the atomic arrangement with the help of the Voronoi-Delaunay methods for the division of space into polyhedra. Thus any complex cavity may be represented as a cluster of contiguous Delaunay simplices. These clusters are revealed by percolation analysis with the application of a special ' delta colouring' of the Voronoi network bonds. This paper presents a classification of all complex cavities discovered in computer models of crystals, liquids and amorphous solids. The number of cavity types is rather large and does not reduce to, say, the five canonical holes of Bernal. The latter occupy less than half of the volume. The greater part of the cavities represent branched chains with built-in rings of simplicial holes, octahedra and so on. Large clusters of more than 10 simplices are characteristic of liquids but they do not occur in amorphous solids.