Finite size effects and ion-ion correlations in electrolyte systems

The correlated motion of ions plays a critical role in determining the ionic conductivity. In the present study we explored the finite size effect on the transport properties under periodic boundary conditions. While the ionic conductivity computed from the Nernst-Einstein relation contains a finite-size error, that from the Green-Kubo relation is size-independent. This allows us to estimate the ion-ion correlations through the box size at which they crossover. Our results suggest viscosity as a dominating factor for the observed deviations from the Nernst-Einstein relation in both molecular dynamics simulations and a number of experiments.