Finite-size effects on the molecular dynamics simulation of fast-ion conductors: A case study of lithium garnet oxide Li7La3Zr2O12

• Phase transition can be captured by the smallest cell size (1 × 1 × 1 or 192 atoms) but study of hysteresis requires larger cells.
• Self-diffusivity, ionic conductivity, and Haven ratio have a weak dependence on the cell size.
• Inverse thermodynamic factor and Fickian diffusivity decreases and increases with the increasing cell sizes respectively.
• A cell size of 3 × 3 × 3 (5184 atoms) is suitable to study Li7La3Zr2O12.

A useful tool to study ionic conduction mechanisms in fast-ion conductors is the molecular dynamics (MD) simulation performed on finite simulation cells with periodic boundary conditions. While there have been many studies of the effect of cell size on the thermodynamics and kinetics of simple liquids, the finite-size effect in fast-ion conductors remains elusive. This work presents a case study to investigate the finite-size effect on the phase transition, self-diffusivity, ionic conductivity, Haven ratio, thermodynamic factor, and Fickian diffusivity using lithium garnet oxide Li7La3Zr2O12 as a model material. It was found that cell sizes influence extracted thermodynamic and kinetic characteristics in different ways with magnitude ranging from weak to strong. For Li7La3Zr2O12, reliable properties can be obtained with a 3 × 3 × 3 (5184 atoms) cell.