Non-equilibrium nucleation and ultrafast growth of ice VII under ramp compression

Abstract

Under ramp compression, water can rapidly freeze into ice VII within nanoseconds, in stark contrast to its freezing behavior under ambient conditions, which typically takes several seconds. Understanding this rapid freezing process is essential for planetary science and high-pressure physics. However, the underlying mechanisms, particularly at the molecular scale, remain poorly understood. Here, we employ deep neural network-based molecular dynamics simulations to investigate the ramp compression of water. Two notable phenomena are observed: (1) extreme ramp compression delays nucleation to pressures exceeding those predicted by classical nucleation theory, indicating non-equilibrium nucleation; (2) the formation of a thermally elevated nucleus and an interfacial layer with high rotational mobility accelerates hydrogen bond rearrangement, thereby facilitating ice growth. Inspired by these findings, a scaling law is proposed to predict the transition pressure to ice VII under ramp compression, revealing that the metastable water can be overdriven far beyond its known limits. By bridging atomistic dynamics with macroscopic phase transitions, our work provides transformative insights into phase transitions under dynamic loading.