Origins and predictability of the hydrostatic limit of molecular liquids

Loss of hydrostaticity limits high-pressure experiments, as pressure transmitting media solidify under compression. Here, we report a strong and positive correlation between the increase of molar density with pressure (ζ) and the hydrostatic limit (HL) associated with the vitrification of isothermally compressed molecular liquids. This correlation is derived using molecular dynamics simulations and is validated against experimental values of ζ and HL. The positive ζ-HL correlation can be rationalized by writing ζ as a function of the molar density (ρ) and the pressure-induced decrease in molar volume (υ): ζ=ρ^{2}υ. While liquids are seen to not exhibit large ρ and υ simultaneously, we find that large HL values originate mostly from large ρ, or, to some extent, from a large υ. At the molecular level, large ρ and large υ are linked to small molecular sizes and to low characteristic frequencies of intermolecular vibrations (ω), respectively.