**Interfacial ion solvation: Obtaining the thermodynamic limit from
molecular simulations**

SJ Cox and PL Geissler, JOURNAL OF CHEMICAL PHYSICS, 148, 222823 (2018).

DOI: 10.1063/1.5020563

Inferring properties of macroscopic solutions from molecular simulations
is complicated by the limited size of systems that can be feasibly
examined with a computer. When long-ranged electrostatic interactions
are involved, the resulting finite size effects can be substantial and
may attenuate very slowly with increasing system size, as shown by
previouswork on dilute ions in bulk aqueous solution. Here we examine
corrections for such effects, with an emphasis on solvation near
interfaces. Our central assumption follows the perspective of
Hunenberger and McCammon **J. Chem. Phys. 110, 1856 (1999)**: Long-
wavelength solvent response underlying finite size effects should be
well described by reduced models like dielectric continuum theory, whose
size dependence can be calculated straightforwardly. Applied to an ion
in a periodic slab of liquid coexisting with vapor, this approach yields
a finite size correction for solvation free energies that differs in
important ways from results previously derived for bulk solution. For a
model polar solvent, we show that this new correction quantitatively
accounts for the variation of solvation free energy with volume and
aspect ratio of the simulation cell. Correcting periodic slab results
for an aqueous system requires an additional accounting for the
solvent's intrinsic charge asymmetry, which shifts electric potentials
in a size-dependent manner. The accuracy of these finite size
corrections establishes a simple method for a posteriori extrapolation
to the thermodynamic limit and also underscores the realism of
dielectric continuum theory down to the nanometer scale. Published by
AIP Publishing.

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