Constant-Current Nonequilibrium Molecular Dynamics Approach for Accelerated Computation of Ionic Conductivity Including Ion-Ion Correlation

Calculation of ionic conductivity including ion-ion correlation effects using equilibrium molecular dynamics (EMD) is computationally demanding, but the correlation is significant in many promising electrolytes such as solid electrolytes. Herein, we have developed a “constant-current” nonequilibrium MD (NEMD) simulation method, in contrast to the conventional constant-field approach, for ion-ion correlated conductivities from a constrained ionic current with fluctuating external field. The improved efficiency of the constant-current NEMD approach is demonstrated by applying it to a representative solid electrolyte, cubic Li_{7}La_{3}Zr_{2}O_{12}. The convergence of the correlated conductivity is faster than that of EMD by 2 orders of magnitude. The low-temperature NEMD simulations also reveal that the ionic conductivity of Li_{7}La_{3}Zr_{2}O_{12} exhibits non-Arrhenius behavior of the activation energy that changes at around 600 K. This work presents not only the high sampling efficiency of constant-current NEMD to calculate the correlated ionic conductivity, but also the importance of direct computations of ionic conductivity at low temperature without Arrhenius extrapolation.