K$^{+}$-hydration in a low-energy two-dimensional wetting layer on the basal surface of muscovite

Density Functional Theory points to a key role of K$^{+}$ solvation in the low-energy two-dimensional arrangement of water molecules on the basal surface of muscovite. At a coverage of 9 water molecules per 2 surface potassium ions, there is room to accommodate the ions into wetting layers wherein half of them are hydrated by 3 and the other half by 4 water molecules, with no broken H-bonds, or wherein all are hydrated by 4. Relative to the ``fully connected network of H-bonded water molecules'' that M. Odelius \textit{et al.}. [Phys. Rev. Lett. \textbf{78}, 2855-- 2858 (1997)] found to form ``a cage around the potassium ions,'' the hydrating arrangements are several tens of meV/H$_{\mathrm{2}}$O better bound. Thus, low-temperature wetting on muscovite is not driven towards ``ice-like'' hexagonal coordination. Instead, solvation forces dominate.\\[4pt]Sandia National Laboratories is a multi-program laboratory managed and operated by Sandia Corporation, a wholly owned subsidiary of Lockheed Martin Corporation, for the U.S. Department of Energy's National Nuclear Security Administration under contract DE-AC04-94AL85000.