Origin of the anisotropic dielectric response of nanoconfined water

For water in slits of height h between atomically flat graphite or hBN walls, the perpendicular dielectric constant falls to $\epsilon_{\mathrm{perp}} \sim 2$ for $h \sim 1\ \mathrm{nm}$ (2018 measurement), while a 2025 measurement found the in-plane constant $\epsilon_{\mathrm{par}}$ of about 1000 at few-layer thickness with superionic-level conductivity. Determine whether a model of interfacial layers with an anisotropic local dielectric tensor reproduces both $\epsilon_{\mathrm{perp}}(h)$ and $\epsilon_{\mathrm{par}}(h)$, or whether nonlocal correlated polarization and proton transport are required. An answer is a first-principles or simulation prediction of $\epsilon_{\mathrm{perp}}(h)$, $\epsilon_{\mathrm{par}}(h)$ and conductivity that matches both data sets.

Ab initio or validated force-field simulations of the measured geometries reproducing both dielectric components and the conductivity versus h, with the controlling molecular feature identified.