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Title: Hydration structure of salt solutions from ab initio molecular dynamics

Abstract

The solvation structures of Na{sup +}, K{sup +}, and Cl{sup -} ions in aqueous solution have been investigated using density functional theory (DFT) based Car-Parrinello (CP) molecular dynamics (MD) simulations. CPMD trajectories were collected for systems containing three NaCl or KCl ion pairs solvated by 122 water molecules using three different but commonly employed density functionals (BLYP, HCTH, and PBE) with electron correlation treated at the level of the generalized gradient approximation (GGA). The effect of including dispersion forces was analyzed through the use of an empirical correction to the DFT-GGA scheme. Special attention was paid to the hydration characteristics, especially the structural properties of the first solvation shell of the ions, which was investigated through ion-water radial distribution functions, coordination numbers, and angular distribution functions. There are significant differences between the present results obtained from CPMD simulations and those provided by classical MD based on either the CHARMM force field or a polarizable model. Overall, the computed structural properties are in fair agreement with the available experimental results. In particular, the observed coordination numbers 5.0-5.5, 6.0-6.4, and 6.0-6.5 for Na{sup +}, K{sup +}, and Cl{sup -}, respectively, are consistent with X-ray and neutron scattering studies but differ somewhat frommore » some of the many other recent computational studies of these important systems. Possible reasons for the differences are discussed.« less

Authors:
; ;  [1]
  1. Institute for Computational Molecular Science and Department of Chemistry, Temple University, Philadelphia, Pennsylvania 19122 (United States)
Publication Date:
OSTI Identifier:
22099162
Resource Type:
Journal Article
Resource Relation:
Journal Name: Journal of Chemical Physics; Journal Volume: 138; Journal Issue: 1; Other Information: (c) 2013 American Institute of Physics; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
37 INORGANIC, ORGANIC, PHYSICAL AND ANALYTICAL CHEMISTRY; 74 ATOMIC AND MOLECULAR PHYSICS; ANGULAR DISTRIBUTION; ANIONS; APPROXIMATIONS; AQUEOUS SOLUTIONS; CATIONS; CHLORINE IONS; DENSITY FUNCTIONAL METHOD; ELECTRON CORRELATION; HYDRATION; ION PAIRS; MOLECULAR DYNAMICS METHOD; NEUTRON DIFFRACTION; POTASSIUM IONS; SIMULATION; SODIUM IONS; X-RAY DIFFRACTION

Citation Formats

Bankura, Arindam, Carnevale, Vincenzo, and Klein, Michael L. Hydration structure of salt solutions from ab initio molecular dynamics. United States: N. p., 2013. Web. doi:10.1063/1.4772761.
Bankura, Arindam, Carnevale, Vincenzo, & Klein, Michael L. Hydration structure of salt solutions from ab initio molecular dynamics. United States. doi:10.1063/1.4772761.
Bankura, Arindam, Carnevale, Vincenzo, and Klein, Michael L. Mon . "Hydration structure of salt solutions from ab initio molecular dynamics". United States. doi:10.1063/1.4772761.
@article{osti_22099162,
title = {Hydration structure of salt solutions from ab initio molecular dynamics},
author = {Bankura, Arindam and Carnevale, Vincenzo and Klein, Michael L.},
abstractNote = {The solvation structures of Na{sup +}, K{sup +}, and Cl{sup -} ions in aqueous solution have been investigated using density functional theory (DFT) based Car-Parrinello (CP) molecular dynamics (MD) simulations. CPMD trajectories were collected for systems containing three NaCl or KCl ion pairs solvated by 122 water molecules using three different but commonly employed density functionals (BLYP, HCTH, and PBE) with electron correlation treated at the level of the generalized gradient approximation (GGA). The effect of including dispersion forces was analyzed through the use of an empirical correction to the DFT-GGA scheme. Special attention was paid to the hydration characteristics, especially the structural properties of the first solvation shell of the ions, which was investigated through ion-water radial distribution functions, coordination numbers, and angular distribution functions. There are significant differences between the present results obtained from CPMD simulations and those provided by classical MD based on either the CHARMM force field or a polarizable model. Overall, the computed structural properties are in fair agreement with the available experimental results. In particular, the observed coordination numbers 5.0-5.5, 6.0-6.4, and 6.0-6.5 for Na{sup +}, K{sup +}, and Cl{sup -}, respectively, are consistent with X-ray and neutron scattering studies but differ somewhat from some of the many other recent computational studies of these important systems. Possible reasons for the differences are discussed.},
doi = {10.1063/1.4772761},
journal = {Journal of Chemical Physics},
number = 1,
volume = 138,
place = {United States},
year = {Mon Jan 07 00:00:00 EST 2013},
month = {Mon Jan 07 00:00:00 EST 2013}
}
  • Ab initio molecular dynamics (AIMD) simulations of the hydration shells surrounding the Zn2+ ion are reported for temperatures near 300oC. Simulations using a combined ab initio and classical molecular dynamics (AIMD/MM) approach are also carried out. Both simulations are done with 64 solvating water molecules (~15 ps). The hydration structure predicted from both simulations is found to agree very well with known results from X-ray data. The 1st hydration shell contains six water molecules in an octahedral structure with the hydrogen atoms oriented away from the Zn2+ ion. The six waters in the 1st shell are located at an averagemore » distance of 2.44Å. A 2nd hydration shell is observed at 4.59Å. Beyond these shells, the bonding pattern substantially returns to the tetrahedral structure of bulk water. No exchanges are seen between the 1st and 2nd hydrations shells, however many water transfers between the 2nd and outer hydrations shells are observed to occur on a picosecond (ps) time scale via dissociative and associative mechanisms. In general, it is found that the AIMD and AIMD/MM simulations give nearly identical results for structural parameters, EXAFS spectra, and exchange dynamics. These results suggest that AIMD/MM can be used to extend the particle scale and time scale of AIMD simulations of highly charged ions in solution.« less
  • We apply DFT+U-based ab initio molecular dynamics simulations to study the hydration structures of U(III) and U(IV) ions, pertinent to redox reactions associated with uranium salts in aqueous media. U(III) is predicted to be coordinated to 8 water molecules, while U(IV) has a hydration number between 7 and 8. At least one of the innershell water molecules of the hydrated U(IV) complex becomes spontaneously deprotonated. As a result, the U(IV)-O pair correlation function exhibits a satellite peak at 2.15 A associated with the shorter U(IV)-(OH{sup -}) bond. This feature is not accounted for in analysis of extended x-ray absorption finemore » structure and x-ray adsorption near edge structure measurements, which yield higher estimates of U(IV) hydration numbers. This suggests that it may be useful to include the effect of possible hydrolysis in future interpretation of experiments, especially when the experimental pH is close to the reported hydrolysis equilibrium constant value.« less
  • The heats of formation for the boron amines BH{sub 3}NH{sub 3}, BH{sub 2}NH{sub 2}, and HBNH, tetrahedral BH{sub 4}{sup -}, and the BN molecule have been calculated by using ab initio molecular orbital theory. Coupled cluster calculations with perturbative triples (CCSD(T)) were employed for the total valence electronic energies. Correlation consistent basis sets were used, up through the augmented quadruple zeta, to extrapolate to the complete basis set limit. Core/valence, scalar relativistic, and spin-orbit corrections were included in an additive fashion to predict the atomization energies. Geometries were calculated at the CCSD(T) level up through at least aug-cc-pVTZ and frequenciesmore » were calculated at the CCSD(T)/aug-cc-pVDZ level. The heats of formation at 0K in the gas phase are {Delta}H{sub f}(BH{sub 3}NH{sub 3}) = -9.1, {Delta}H{sub f}(BH{sub 2}NH{sub 2}) = -15.9, {Delta}H{sub f}(BHNH) = 13.6, {Delta}H{sub f}(BN) = 146.4, and {Delta}H{sub f}(BH{sub 4}{sup -}) = -11.6 kcal/mol. The reported experimental value for {Delta}H{sub f}(BN) is clearly in error. The heat of formation of the salt [BH{sub 4}{sup -}NH{sub 4}{sup +}] (s) has been estimated by using an empirical expression for the lattice energy and the calculated heats of formation of the two component ions. The calculations show that both BH{sub 3}NH{sub 3}(g) and [BH{sub 4}{sup -}][NH{sub 4}{sup +}](s) can serve as good hydrogen storage systems which release H{sub 2} in a slightly exothermic process. The hydride affinity of BH{sub 3} is calculated to be 72.2 kcal/mol in excellent agreement with the experimental value at 298K of 74.2 {+-} 2.8 kcal/mol.« less