Fausto Martelli
IBM Research Laboratory, United Kingdom
I inspect the origin of water’s anomalies simulating the isobaric cooling of a sample composed of 512 water molecules from ambient to deeply undercooled conditions at three pressures, namely, 1 bar, 400 bars, and 1000 bars. At temperatures above the Widom line (WL) the system is characterised by a large HDL-like cluster spanning the entire simulation box and accommodating few small, disconnected LDL-like environments. On the other hand, in correspondence with the WL, the HDL-like dominating cluster undergoes fragmentation caused by the percolation of LDL-like aggregates following a spinodal-like kinetics. Remarkably, such fragmentation always occurs at a “critical” concentration of ∼20%–30% in LDL, in which LDL-like environments is characterised by an equal number of pentagonal and hexagonal rings that create a state of maximal frustration between a configuration that promotes crystallisation (hexagonal ring) and a configuration that hinders it (pentagonal ring).
F. Martelli, Unravelling the contribution of local structures to the anomalies of water: The synergistic action of several factors, J. Chem. Phys. 150, 094506 (2019)