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

TL;DR

This study reveals a nonmonotonic relationship between absolute entropy and temperature in supercooled Stillinger-Weber silicon, highlighting complex thermodynamic behavior near 1060 K through precise free energy calculations.

Contribution

It introduces a thermodynamic integration method to accurately compute excess Gibbs free energy and uncovers nonmonotonic entropy behavior in supercooled silicon.

Findings

Entropy increases as temperature decreases from 1065 K to 1060 K.

Volume distribution broadens and exhibits VDW loops near 1060 K.

Insights into the phase transition from HDL to low-density phases.

Abstract

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.