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Title: Quasichemical analysis of the cluster-pair approximation for the thermodynamics of proton hydration

Abstract

A theoretical analysis of the cluster-pair approximation (CPA) is presented based on the quasichemical theory of solutions. The sought single-ion hydration free energy of the proton includes an interfacial potential contribution by definition. It is shown, however, that the CPA involves an extra-thermodynamic assumption that does not guarantee uniform convergence to a bulk free energy value with increasing cluster size. A numerical test of the CPA is performed using the classical polarizable AMOEBA force field and supporting quantum chemical calculations. The enthalpy and free energy differences are computed for the kosmotropic Na{sup +}/F{sup −} ion pair in water clusters of size n = 5, 25, 105. Additional calculations are performed for the chaotropic Rb{sup +}/I{sup −} ion pair. A small shift in the proton hydration free energy and a larger shift in the hydration enthalpy, relative to the CPA values, are predicted based on the n = 105 simulations. The shifts arise from a combination of sequential hydration and interfacial potential effects. The AMOEBA and quantum chemical results suggest an electrochemical surface potential of water in the range −0.4 to −0.5 V. The physical content of single-ion free energies and implications for ion-water force field development are also discussed.

Authors:
 [1];  [1]
  1. Department of Chemistry, University of Cincinnati, Cincinnati, Ohio 45221 (United States)
Publication Date:
OSTI Identifier:
22420087
Resource Type:
Journal Article
Journal Name:
Journal of Chemical Physics
Additional Journal Information:
Journal Volume: 140; Journal Issue: 22; Other Information: (c) 2014 AIP Publishing LLC; Country of input: International Atomic Energy Agency (IAEA); Journal ID: ISSN 0021-9606
Country of Publication:
United States
Language:
English
Subject:
37 INORGANIC, ORGANIC, PHYSICAL AND ANALYTICAL CHEMISTRY; ENTHALPY; FREE ENERGY; HYDRATION; ION PAIRS; PROTONS; RUBIDIUM IONS; SIMULATION; SODIUM IONS; SOLUTIONS; SURFACE POTENTIAL; THERMODYNAMICS; WATER

Citation Formats

Pollard, Travis, Beck, Thomas L., and Department of Physics, University of Cincinnati, Cincinnati, Ohio 45221. Quasichemical analysis of the cluster-pair approximation for the thermodynamics of proton hydration. United States: N. p., 2014. Web. doi:10.1063/1.4881602.
Pollard, Travis, Beck, Thomas L., & Department of Physics, University of Cincinnati, Cincinnati, Ohio 45221. Quasichemical analysis of the cluster-pair approximation for the thermodynamics of proton hydration. United States. https://doi.org/10.1063/1.4881602
Pollard, Travis, Beck, Thomas L., and Department of Physics, University of Cincinnati, Cincinnati, Ohio 45221. 2014. "Quasichemical analysis of the cluster-pair approximation for the thermodynamics of proton hydration". United States. https://doi.org/10.1063/1.4881602.
@article{osti_22420087,
title = {Quasichemical analysis of the cluster-pair approximation for the thermodynamics of proton hydration},
author = {Pollard, Travis and Beck, Thomas L. and Department of Physics, University of Cincinnati, Cincinnati, Ohio 45221},
abstractNote = {A theoretical analysis of the cluster-pair approximation (CPA) is presented based on the quasichemical theory of solutions. The sought single-ion hydration free energy of the proton includes an interfacial potential contribution by definition. It is shown, however, that the CPA involves an extra-thermodynamic assumption that does not guarantee uniform convergence to a bulk free energy value with increasing cluster size. A numerical test of the CPA is performed using the classical polarizable AMOEBA force field and supporting quantum chemical calculations. The enthalpy and free energy differences are computed for the kosmotropic Na{sup +}/F{sup −} ion pair in water clusters of size n = 5, 25, 105. Additional calculations are performed for the chaotropic Rb{sup +}/I{sup −} ion pair. A small shift in the proton hydration free energy and a larger shift in the hydration enthalpy, relative to the CPA values, are predicted based on the n = 105 simulations. The shifts arise from a combination of sequential hydration and interfacial potential effects. The AMOEBA and quantum chemical results suggest an electrochemical surface potential of water in the range −0.4 to −0.5 V. The physical content of single-ion free energies and implications for ion-water force field development are also discussed.},
doi = {10.1063/1.4881602},
url = {https://www.osti.gov/biblio/22420087}, journal = {Journal of Chemical Physics},
issn = {0021-9606},
number = 22,
volume = 140,
place = {United States},
year = {Sat Jun 14 00:00:00 EDT 2014},
month = {Sat Jun 14 00:00:00 EDT 2014}
}