Nonmonotonic dependence of the absolute entropy on temperature in supercooled Stillinger-Weber silicon

Using a recently developed thermodynamic integration method, we compute the precise values of the excess Gibbs free energy (G^e) of the high density liquid (HDL) phase with respect to the crystalline phase at different temperatures (T) in the supercooled region of the Stillinger-Weber (SW) silicon [F. H. Stillinger and T. A. Weber, Phys. Rev. B. 32, 5262 (1985)]. Based on the slope of G^e with respect to T, we find that the absolute entropy of the HDL phase increases as its enthalpy changes from the equilibrium value at T \ge 1065 K to the value corresponding to a non-equilibrium state at 1060 K. We find that the volume distribution in the equilibrium HDL phases become progressively broader as the temperature is reduced to 1060 K, exhibiting van-der-Waals (VDW) loop in the pressure-volume curves. Our results provides insight into the thermodynamic cause of the transition from the HDL phase to the low density phases in SW silicon, observed in earlier studies near 1060 K at zero pressure.Comment: This version is accepted for publication in Journal of Statistical Physics (11 figures, 1 table

Quantum effects in dynamics of water and other liquids of light molecules

Nuclear quantum effects in atomic motions are well known at low temperatures $T 50-100$ K. Recent studies, however, suggested that nuclear quantum effects in systems of light molecules (e.g., water) might play an important role in structural dynamics and provide non-negligible contributions at such temperatures, and even up to ambient temperature. In this article, we discuss experimental evidences of the quantum effects in glass transition in liquids of light molecules and possible theoretical descriptions of these effects. We show that quantum effects may qualitatively change the temperature behavior of the structural relaxation time in supercooled liquids leading to deviations of some well-established properties of the glass transition when it happens at low temperatures. We also demonstrate that unusual behavior of water dynamics at low temperatures, including apparent fragile-to-strong crossover, can be ascribed to nuclear quantum effects