The theory of transport in highly inhomogeneous systems, developed recently by Pozhar and Gubbins, and the nonequilibrium molecular dynamics (NEMD) technique are employed to study the viscosity of WCA fluids confined in narrow slit pores of width 5.1 and 20σ at reduced densities ρσ3 of 0.422–0.713. Calculated quantities include the equilibrium and nonequilibrium density profiles, equilibrium pair correlation functions, flow velocity profiles, and the viscosity profiles. NEMD simulation results are compared with the theoretical predictions. The agreement is good except for the region within one molecular diameter from the walls. The viscosity was found to vary with position across the pore.

Garnet-structured Li₇La₃Zr₂O₁₂ is a promising solid electrolyte for next-generation solid-state Li batteries. However, sufficiently fast Li-ion mobility required for battery applications only emerges at high temperatures, upon a phase transition to cubic structure. A well-known strategy to stabilize the cubic phase at room temperature relies on aliovalent substitution; in particular, the substitution of Li⁺ by Al³⁺ and Ga³⁺ ions. Yet, despite having the same formal charge, Ga³⁺ substitution yields higher conductivities (10^-3 S/cm) than Al³⁺ (10^-4 S/cm). The reason of such difference in ionic conductivity remains a mystery. Here we use molecular dynamic simulations and advanced sampling techniques to precisely unveil the atomistic origin of this phenomenon. Our results show that Li⁺ vacancies generated by Al³⁺ and Ga³⁺ substitution remain adjacent to Ga³⁺ and Al³⁺ ions, without contributing to the promotion of Li⁺ mobility. However, while Ga³⁺ ions tend to allow limited Li⁺ diffusion within their immediate surroundings, the less repulsive interactions associated with Al³⁺ ions lead to a complete blockage of neighboring Li⁺ diffusion paths. This effect is magnified at lower temperatures, and explains the higher conductivities observed for Ga-substituted systems. Overall this study provides a valuable insight into the fundamental ion transport mechanism in the bulk of Ga/Al-substituted Li₇La₃Zr₂O₁₂ and paves the way for rationalizing aliovalent substitution design strategies for enhancing ionic transport in these materials.

Modern atto-second experiments seek to provide an insight into a long standing question: “how much time does a tunnelling particle spend in the barrier?” Traditionally, quantum theory relates this duration to the delay with which the particle emerges from the barrier. The link between these two times is self-evident in classical mechanics, but may or may not exist in the quantum case. Here we show that it does not, and give a detailed explanation why. The tunnelling process does not lend itself to classical analogies, and its duration cannot, in general, be guessed by observing the behaviour of the transmitted particle.

This work provides solid guidance for the selection of accurate and robust vdW-inclusive methods for high-throughput computational screening of layered electroactive materials.