  The two-phase thermodynamic (2PT) model {[}J. Chem. Phys., \textbf{119},
11792 (2003){]} provides a promising paradigm to efficiently determine the
ionic entropies of liquids from molecular dynamics (MD). In this model, the
vibrational density of states (VDoS) of a liquid is decomposed into a diffusive
gas-like component and a vibrational solid-like component. By treating the
diffusive component as hard sphere (HS) gas and the vibrational component as
harmonic oscillators, the ionic entropy of the liquid is determined. Here we
examine three issues crucial for practical implementations of the 2PT model:
(i) the mismatch between the VDoS of the liquid system and that of the HS gas;
(ii) the excess entropy of the HS gas; (iii) the partition of the gas-like and
solid-like components. Some of these issues have not been addressed before, yet
they profoundly change the entropy predicted from the model. Based on these
findings, a revised 2PT formalism is proposed and successfully tested in
systems with Lennard-Jones potentials as well as many-atom potentials of liquid
metals. Aside from being capable of performing quick entropy estimations for a
wide range of systems, the formalism also supports fine-tuning to accurately
determine entropies at specific thermal states.

Chemical Physics;Statistical Mechanics