A polymerization scenario of the liquid-liquid transition of GeI₄

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 [Formula: see text] 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.