Distinguishing liquids from amorphous solids: Percolation analysis on the Voronoi network

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Abstract
The mutual arrangement of the Delaunay simplices (configurations of four nearest atoms) has been studied for molecular dynamic (MD) models of liquid and quenched rubidium obtained by M. Tanaka [J. Phys. Soc. Jpn. 5 5, 3108 (1986)]. The Delaunay simplices with large circumradii and low local density of atoms, the simplices with small circumradii representing dense atomic configurations, and the simplices close in shape to perfect tetrahedron representing ‘‘rigid’’ arrangements of atomic quadruplets were delineated. The Delaunay simplices form clusters; consideration of the latter constitutes a site percolation problem on the Voronoi network [N. N. Medvedev, V. P. Voloshin, and Yu. I. Naberukhin, J. Phys. A: Math. Gen. 2 1, L247 (1986)]. Analysis of the MD results in these terms shows that low density atomic configurations in the liquid phase form a percolative cluster. Such a cluster does not occur in a solid phase. On the contrary, there is a percolative cluster in the solid sample, but formed by high density configurations which are nearly tetrahedral.