Nuclear quantum effects on structure and thermal conductivity of superionic ice

Abstract

The structural properties and thermal transport of superionic ice are critical to understanding the ice giant planets. However, their nuclear quantum effects (NQEs) remain unknown. Here, we systematically investigated the NQEs of body-centered cubic superionic ice based on a deep potential model combined with path-integral molecular dynamics simulations. The NQEs are found to significantly modify the structural properties of superionic ice. The quantum delocalization of protons leads to a contraction of the oxygen lattice. The radial distribution function analysis reveals that NQEs cause a leftward shift of the O–O peak, elongation of the O–H bond, merger of the H–H peaks, and anomalous temperature independence of the first O–H and H–H peaks. The total thermal conductivity obtained from quantum simulations is significantly higher than that from classical simulations, with the primary contribution arising from the enhanced heat convection due to proton diffusion rather than from heat conduction dominated by lattice vibrations. This study elucidates the microscopic mechanism of NQE-regulated thermal transport in superionic ice through the enhancement of proton convection, providing an important quantum-correction basis for modeling the thermal physical properties of ice under extreme conditions.