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Open AccessArticle

Entropy of Simulated Liquids Using Multiscale Cell Correlation

Manchester Institute of Biotechnology, The University of Manchester, 131 Princess Street, Manchester M1 7DN, UK
School of Chemistry, The University of Manchester, Oxford Road, Manchester M13 9PL, UK
Author to whom correspondence should be addressed.
Human Genetics Unit, Institute of Genetics & Molecular Medicine, The University of Edinburgh, Western General Hospital, Crewe Road South, Edinburgh EH4 2XU, UK.
Entropy 2019, 21(8), 750;
Received: 29 June 2019 / Revised: 22 July 2019 / Accepted: 28 July 2019 / Published: 31 July 2019
Accurately calculating the entropy of liquids is an important goal, given that many processes take place in the liquid phase. Of almost equal importance is understanding the values obtained. However, there are few methods that can calculate the entropy of such systems, and fewer still to make sense of the values obtained. We present our multiscale cell correlation (MCC) method to calculate the entropy of liquids from molecular dynamics simulations. The method uses forces and torques at the molecule and united-atom levels and probability distributions of molecular coordinations and conformations. The main differences with previous work are the consistent treatment of the mean-field cell approximation to the approriate degrees of freedom, the separation of the force and torque covariance matrices, and the inclusion of conformation correlation for molecules with multiple dihedrals. MCC is applied to a broader set of 56 important industrial liquids modeled using the Generalized AMBER Force Field (GAFF) and Optimized Potentials for Liquid Simulations (OPLS) force fields with 1.14*CM1A charges. Unsigned errors versus experimental entropies are 8.7 J K 1 mol 1 for GAFF and 9.8 J K 1 mol 1 for OPLS. This is significantly better than the 2-Phase Thermodynamics method for the subset of molecules in common, which is the only other method that has been applied to such systems. MCC makes clear why the entropy has the value it does by providing a decomposition in terms of translational and rotational vibrational entropy and topographical entropy at the molecular and united-atom levels. View Full-Text
Keywords: structure; thermodynamics; probability distribution; force; torque; coordination; conformation; molecular dynamics simulation structure; thermodynamics; probability distribution; force; torque; coordination; conformation; molecular dynamics simulation
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Ali, H.S.; Higham, J.; Henchman, R.H. Entropy of Simulated Liquids Using Multiscale Cell Correlation. Entropy 2019, 21, 750.

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