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The Born Model Can Accurately Describe Electrostatic Ion Solvation.

preprint
submitted on 13.07.2020 and posted on 14.07.2020 by Timothy Duignan, Xiu Song Zhao

Accurate models of the free energies of ions in solution are crucial for understanding and modelling the huge number of important applications where electrolyte solutions play a crucial role such as electrochemical energy storage. The Born model, developed to describe ion solvation free energies, is widely considered to be critically flawed as it predicts a linear response of water to ionic charge, which fails to match water's supposed intrinsic preference to solvate anions over cations. Here, we demonstrate that this asymmetric response observed in simulation is the result of an arbitrary choice that the oxygen atom should be the centre of a water molecule. We show that an alternative and reasonable choice, which places the centre 0.5 Å towards the hydrogen atoms, results in a linear and charge symmetric response of water to ionic charge for a classical water model consistent with the Born model. This asymmetry should therefore be regarded as a property of the short range repulsive interaction not an intrinsic electrostatic property of water. We also show that this new water centre results in a more reasonable neutral cavity potential.

Funding

Australian Research Council

History

Email Address of Submitting Author

t.duignan@uq.edu.au

Institution

University of Queensland

Country

Australia

ORCID For Submitting Author

0000-0003-3772-8057

Declaration of Conflict of Interest

None

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