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Correlations in liquid water for the TIP3P-Ewald, TIP4P-2005, TIP5P-Ewald, and SWM4-NDP models.


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Authors

Huggins, David J 

Abstract

Water is one of the simplest molecules in existence, but also one of the most important in biological and engineered systems. However, understanding the structure and dynamics of liquid water remains a major scientific challenge. Molecular dynamics simulations of liquid water were performed using the water models TIP3P-Ewald, TIP4P-2005, TIP5P-Ewald, and SWM4-NDP to calculate the radial distribution functions (RDFs), the relative angular distributions, and the excess enthalpies, entropies, and free energies. In addition, lower-order approximations to the entropy were considered, identifying the fourth-order approximation as an excellent estimate of the full entropy. The second-order and third-order approximations are ~20% larger and smaller than the true entropy, respectively. All four models perform very well in predicting the radial distribution functions, with the TIP5P-Ewald model providing the best match to the experimental data. The models also perform well in predicting the excess entropy, enthalpy, and free energy of liquid water. The TIP4P-2005 and SWM4-NDP models are more accurate than the TIP3P-Ewald and TIP5P-Ewald models in this respect. However, the relative angular distribution functions of the four water models reveal notable differences. The TIP5P-Ewald model demonstrates an increased preference for water molecules to act both as tetrahedral hydrogen bond donors and acceptors, whereas the SWM4-NDP model demonstrates an increased preference for water molecules to act as planar hydrogen bond acceptors. These differences are not uncovered by analysis of the RDFs or the commonly employed tetrahedral order parameter. However, they are expected to be very important when considering water molecules around solutes and are thus a key consideration in modelling solvent entropy.

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Keywords

Entropy, Hydrogen Bonding, Molecular Dynamics Simulation, Thermodynamics, Water

Journal Title

J Chem Phys

Conference Name

Journal ISSN

0021-9606
1089-7690

Volume Title

136

Publisher

AIP Publishing
Sponsorship
Engineering and Physical Sciences Research Council (EP/F032773/1)
Medical Research Council (G0700651)
Medical Research Council (G1001522)
Wellcome Trust (091058/Z/09/C)
Wellcome Trust (091058/Z/09/Z)
Acknowledgements go to Mike Payne for careful reading of the paper; Peter Freddolino, Chris Baker, David Payne, and Bracken King for helpful discussions; Stuart Rankin for technical help; and the NVIDIA CUDA Centre of Excellence at the Cambridge HPCS for use of the CUDA-accelerated GPUs. Thanks also go to the reviewers for their helpful comments. All calculations were performed using the Darwin Supercomputer of the University of Cambridge High Performance Computing Service (http://www.hpc.cam.ac.uk/) provided by Dell Inc. using Strategic Research Infrastructure Funding from the Higher Education Funding Council for England and were funded by the Engineering and Physical Sciences Research Consul (United Kingdom) (EPSRC) under Grant No. EP/F032773/1. Thanks for financial support go to the MRC, Wellcome Trust, and EPSRC.