Theoretical study of Na+ transport in the solid-state electrolyte Na3OBr based on deep potential molecular dynamics

Abstract

Recent discoveries in the antiperovskite-class sodium superionic conductors call for a thorough molecular dynamics (MD) study of sodium ion mobility, but the practical use of MD is often hindered by the accuracy-vs.-efficiency dilemma. Here we applied the recently developed deep potential molecular dynamics (DeePMD) approach to investigate the ion mobility in Na₃OBr. With the deep potential model for Na₃OBr constructed based on first-principles density-functional theory (DFT) calculations, we directly calculate the Na⁺ diffusion coefficient at various temperatures, and obtain an activation energy of 0.42–0.43 eV. This in comparison with the 0 K migration barrier (0.41–0.43 eV) suggests that the finite temperature effect is negligible for Na₃OBr. The model gives an extrapolated room temperature ionic conductivity of 1 × 10⁻⁴–2 × 10⁻⁴ mS cm⁻¹, roughly in the same order of magnitude as the experimental results. We also confirm the proportionality of the diffusion coefficient with respect to the vacancy concentration, and find that the migration barrier is relatively insensitive to the vacancy concentration. This work further demonstrates the promising role of the DeePMD method in the study of the transport properties of solid-state electrolytes.