Quantifying the Impact of Electric Fields on the Local Structure and Migration of Potassium Ions at the Orthoclase (001) Surface

Developing an understanding of the response of mineral/water interfaces to applied electric fields is central to detecting and interpreting signatures of interfacial processes in the subsurface. Here, we focus density functional theory calculations on understanding K+cation binding and migration across the (001) surface of orthoclase feldspar under various applied electric fields with and without surface hydration. The calculations reveal how water ligands labilize surface K+cations for migration while also increasing their sensitivity to electric field effects on the binding energy at different surface sites. The calculations also show how the direction and strength of the electric field systematically affect surface cation mobility, sorption, and hydration behavior. Specifically, electric fields directed toward the surface reduce the energy gap between the different surface potassium sites, favor hydration, and shorten K+residence time at their crystallographic site. The findings help fill a major knowledge gap in the impact of electric fields on mineral/water interface structure and dynamics more generally, featuring, in this case, a commonly found type of feldspar involved in a multitude of atmospheric and geochemical processes.