TY - JOUR
T1 - Activity coefficients of aqueous electrolytes from implicit-water molecular dynamics simulations
AU - Saravi, Sina Hassanjani
AU - Panagiotopoulos, Athanassios Z.
N1 - Funding Information:
The authors would like to acknowledge the European Research Council (ERC) for funding this research under the European Union’s Horizon 2020 research and innovation program (Grant Agreement No. 832460), ERC Advanced Grant project “New Paradigm in Electrolyte Thermodynamics.” Additional support was provided by the Princeton Center for Complex Materials, a U.S. National Science Foundation Materials Research Science and Engineering Center (Award No. DMR-1420541). Simulations were performed using computational resources supported by the Princeton Institute for Computational Science and Engineering (PIC-SciE) and the Office of Information Technology’s High Performance Computing Center at Princeton University.
Publisher Copyright:
© 2021 Author(s).
PY - 2021/11/14
Y1 - 2021/11/14
N2 - We obtain activity coefficients in NaCl and KCl solutions from implicit-water molecular dynamics simulations, at 298.15 K and 1 bar, using two distinct approaches. In the first approach, we consider ions in a continuum with constant relative permittivity (ɛr) equal to that of pure water; in the other approach, we take into account the concentration-dependence of ɛr, as obtained from explicit-water simulations. Individual ion activity coefficients (IIACs) are calculated using gradual insertion of single ions with uniform neutralizing backgrounds to ensure electroneutrality. Mean ionic activity coefficients (MIACs) obtained from the corresponding IIACs in simulations with constant ɛr show reasonable agreement with experimental data for both salts. Surprisingly, large systematic negative deviations are observed for both IIACs and MIACs in simulations with concentration-dependent ɛr. Our results suggest that the absence of hydration structure in implicit-water simulations cannot be compensated by correcting for the concentration-dependence of the relative permittivity ɛr. Moreover, even in simulations with constant ɛr for which the calculated MIACs are reasonable, the relative positioning of IIACs of anions and cations is incorrect for NaCl. We conclude that there are severe inherent limitations associated with implicit-water simulations in providing accurate activities of aqueous electrolytes, a finding with direct relevance to the development of electrolyte theories and to the use and interpretation of implicit-solvent simulations.
AB - We obtain activity coefficients in NaCl and KCl solutions from implicit-water molecular dynamics simulations, at 298.15 K and 1 bar, using two distinct approaches. In the first approach, we consider ions in a continuum with constant relative permittivity (ɛr) equal to that of pure water; in the other approach, we take into account the concentration-dependence of ɛr, as obtained from explicit-water simulations. Individual ion activity coefficients (IIACs) are calculated using gradual insertion of single ions with uniform neutralizing backgrounds to ensure electroneutrality. Mean ionic activity coefficients (MIACs) obtained from the corresponding IIACs in simulations with constant ɛr show reasonable agreement with experimental data for both salts. Surprisingly, large systematic negative deviations are observed for both IIACs and MIACs in simulations with concentration-dependent ɛr. Our results suggest that the absence of hydration structure in implicit-water simulations cannot be compensated by correcting for the concentration-dependence of the relative permittivity ɛr. Moreover, even in simulations with constant ɛr for which the calculated MIACs are reasonable, the relative positioning of IIACs of anions and cations is incorrect for NaCl. We conclude that there are severe inherent limitations associated with implicit-water simulations in providing accurate activities of aqueous electrolytes, a finding with direct relevance to the development of electrolyte theories and to the use and interpretation of implicit-solvent simulations.
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U2 - 10.1063/5.0064963
DO - 10.1063/5.0064963
M3 - Article
C2 - 34773944
AN - SCOPUS:85119211952
VL - 155
JO - Journal of Chemical Physics
JF - Journal of Chemical Physics
SN - 0021-9606
IS - 18
M1 - 184501
ER -