Exploring no man's land with simulations at coupled cluster quality

by Wang, Feng; Li, Yaping; Li, Jicun

Water has many anomalies that evade simple explanations. One theory that explains the anomalies predicts the existence of a liq.-liq. phase transition (LLPT) in the supercooled region. Unfortunately, the LLPT happens in a region of phase space commonly referred to as "no man's land". It is very challenging to explore this part of the phase space exptl. due to fast nucleation of ice below the homogenous nucleation temp. We present microsecond time scale simulations in the "no man's land" using a force field that is trained to electronic structure calcns. performed at the coupled cluster quality. Our simulation reveals two liq. phases of water sepd. by a first order phase transition with a crit. point at approx. 207 K and 50 MPa. Normal water is the high d. liq. (HDL). The emerging phase is low d. liq. (LDL). LDL has a d. only slightly larger than that of the ice-Ih and shows more long range order than HDL. However, the transformation from LDL to HDL is spontaneous across the first order phase transition line suggesting the LDL configuration is not poorly formed nano-cryst. ice.