A polymerization scenario of the liquid–liquid transition of GeI4

Abstract

SnI4 and GeI4 have been shown to exhibit similar polyamorphic nature. We examine the microscopic nature of the liquid–liquid transition in GeI4 by conducting an isothermal–isobaric molecular dynamics simulation for the system composed of rigid tetrahedral molecules. The model allows us to semiquantitatively discuss the structural properties of liquid GeI4 below 1 GPa. We define a physical bond between the nearest intermolecular iodine sites satisfying the conditions of forming the metallic I2 bond. We then focus on the formation of molecular clusters in dynamic networks of the bonds. The clusters are mainly formed by molecules whose nearest pairs are in edge-to-edge, face-to-edge, and vertex-to-edge orientations. The clusters grow as pressure increases, and the onset of percolation is observed below 1 GPa. The finite-size scaling analysis for the percolation probability identifies that the threshold pressure is GPa for the present model, which is near the extension of the boundary between the two liquid phases. We thus speculate that the liquid–liquid transition of GeI4 is attained by polymerization, i.e. percolation of molecular networks. The same percolation scenario with a slight modification such as introducing a bootstrap mechanism is expected to apply to the transition in liquid SnI4.