Electrostatic solvation free energies of charged hard spheres using molecular dynamics with density functional theory interactions
Abstract
Determining the solvation free energies of single ions in water is one of the most fundamental problems in physical chemistry and yet many unresolved questions remain. In particular, the ability to decompose the solvation free energy into simple and intuitive contributions will have important implications for coarse grained models of electrolyte solution. Here, we provide rigorous definitions of the various types of single ion solvation free energies based on different simulation protocols. We calculate solvation free energies of charged hard spheres using density functional theory interaction potentials with molecular dynamics simulation (DFTMD) and isolate the effects of charge and cavitation, comparing to the Born (linear response) model. We show that using uncorrected Ewald summation leads to highly unphysical values for the solvation free energy and that charging free energies for cations are approximately linear as a function of charge but that there is a small nonlinearity for small anions. The charge hydration asymmetry (CHA) for hard spheres, determined with quantum mechanics, is much larger than for the analogous real ions. This suggests that real ions, particularly anions, are significantly more complex than simple charged hard spheres, a commonly employed representation. We would like to thank Thomas Beck, Shawn Kathmann, Richardmore »
 Authors:
 Physical Science Division, Pacific Northwest National Laboratory, P.O. Box 999, Richland, Washington 99352, USA
 Department of Chemical Engineering, University of Washington, Seattle, Washington 98185, USA
 Publication Date:
 Research Org.:
 Pacific Northwest National Lab. (PNNL), Richland, WA (United States)
 Sponsoring Org.:
 USDOE
 OSTI Identifier:
 1422317
 Report Number(s):
 PNNLSA123710
Journal ID: ISSN 00219606; KC0301050
 DOE Contract Number:
 AC0576RL01830
 Resource Type:
 Journal Article
 Resource Relation:
 Journal Name: Journal of Chemical Physics; Journal Volume: 147; Journal Issue: 16
 Country of Publication:
 United States
 Language:
 English
Citation Formats
Duignan, Timothy T., Baer, Marcel D., Schenter, Gregory K., and Mundy, Chistopher J. Electrostatic solvation free energies of charged hard spheres using molecular dynamics with density functional theory interactions. United States: N. p., 2017.
Web. doi:10.1063/1.4994912.
Duignan, Timothy T., Baer, Marcel D., Schenter, Gregory K., & Mundy, Chistopher J. Electrostatic solvation free energies of charged hard spheres using molecular dynamics with density functional theory interactions. United States. doi:10.1063/1.4994912.
Duignan, Timothy T., Baer, Marcel D., Schenter, Gregory K., and Mundy, Chistopher J. 2017.
"Electrostatic solvation free energies of charged hard spheres using molecular dynamics with density functional theory interactions". United States.
doi:10.1063/1.4994912.
@article{osti_1422317,
title = {Electrostatic solvation free energies of charged hard spheres using molecular dynamics with density functional theory interactions},
author = {Duignan, Timothy T. and Baer, Marcel D. and Schenter, Gregory K. and Mundy, Chistopher J.},
abstractNote = {Determining the solvation free energies of single ions in water is one of the most fundamental problems in physical chemistry and yet many unresolved questions remain. In particular, the ability to decompose the solvation free energy into simple and intuitive contributions will have important implications for coarse grained models of electrolyte solution. Here, we provide rigorous definitions of the various types of single ion solvation free energies based on different simulation protocols. We calculate solvation free energies of charged hard spheres using density functional theory interaction potentials with molecular dynamics simulation (DFTMD) and isolate the effects of charge and cavitation, comparing to the Born (linear response) model. We show that using uncorrected Ewald summation leads to highly unphysical values for the solvation free energy and that charging free energies for cations are approximately linear as a function of charge but that there is a small nonlinearity for small anions. The charge hydration asymmetry (CHA) for hard spheres, determined with quantum mechanics, is much larger than for the analogous real ions. This suggests that real ions, particularly anions, are significantly more complex than simple charged hard spheres, a commonly employed representation. We would like to thank Thomas Beck, Shawn Kathmann, Richard Remsing and John Weeks for helpful discussions. Computing resources were generously allocated by PNNL's Institutional Computing program. This research also used resources of the National Energy Research Scientific Computing Center, a DOE Office of Science User Facility supported by the Office of Science of the U.S. Department of Energy under Contract No. DEAC0205CH11231. TTD, GKS, and CJM were supported by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences, Division of Chemical Sciences, Geosciences, and Biosciences. MDB was supported by MS3 (Materials Synthesis and Simulation Across Scales) Initiative, a Laboratory Directed Research and Development Program at Pacific Northwest National Laboratory (PNNL). PNNL is a multiprogram national laboratory operated by Battelle for the U.S. Department of Energy.},
doi = {10.1063/1.4994912},
journal = {Journal of Chemical Physics},
number = 16,
volume = 147,
place = {United States},
year = 2017,
month =
}

Solvation free energy calculations using continuum dielectric model for the solvent and gradientcorrected density functional theory for the solute
Electrostatic solvation free energies are calculated using a self consistent reaction field (SCRF) procedure that combines a continuum dielectric model of the solvent with both HartreeFock (HF) and density functional theory (DFT) for the solute. Several molecules are studied in aqueous solution. They comprise three groups: nonpolar neutral, polar neutral, and ionic. The calculated values of {Delta}G{sup e1} are sensitive to the atomic radii used to define the solute molecular surface, particularly to the value of the hydrogen radius. However, the values of {Delta}G{sup e1} exhibit reasonable correlation with experiment when a previously determined, physically motivated set of atomic radiimore » 
Density functional theory of molecular fluids: Freeenergy model for the inhomogeneous hardbody fluid
By capturing the correct geometrical features, the [ital fundamental][ital measure] freeenergy density functional [Y. Rosenfeld, Phys. Rev. Lett. [bold 63], 980 (1989); J. Chem. Phys. [bold 98], 8126 (1993)] leads to an accurate description of the general inhomogeneous simple ( atomic'') fluid. It is based on the [ital convolution] [ital decomposition] of the excluded volume for a pair of spheres in terms of characteristic functions for the geometry of the individual spheres. By relating that convolution decomposition for spheres with the [ital Gauss][ital Bonnet] [ital theorem] for general convex bodies, the fundamentalmeasure functional is made applicable to fluids of asymmetricmore » 
Electrostatic potentials and free energies of solvation of polar and charged molecules
Theories of solvation free energies often involve electrostatic potentials at the position of a solute charge. Simulation calculations that apply cutoffs and periodic boundary conditions based on molecular centers result in centerdependent contributions to electrostatics energies due to a systematic sorting of charges in radial shells. This sorting of charges induces a surfacecharge density at the cutoff sphere or simulationbox boundary that depends on the choice of molecular centers. We identify a simple solution that gives correct, centerindependent results, namely the radial integration of charge densities. Our conclusions are illustrated for a LennardJones solute in water. The present results canmore » 
Free Energy Calculations of Crystalline Hard Sphere Complexes Using Density Functional Theory
Recently developed fundamental measure density functional theory (FMT) is used to study binary hard sphere (HS) complexes in crystalline phases. By comparing the excess free energy, pressure and phase diagram, we show that the fundamental measure functional yields good agreements to the available simulation results of AB, AB _{2} and AB _{13} crystals. Additionally, we use this functional to study the HS models of five binary crystals, Cu _{5}Zr(C15 _{b}), Cu _{51}Zr _{14}(β), Cu _{10}Zr _{7}(φ), CuZr(B2) and CuZr _{2} (C11 _{b}), which are observed in the CuZr system. The FMT functional gives well behaved minimum for most of themore »Cited by 2