First principles and molecular dynamics study of Li wetting and diffusion on W surfaces

Abstract Surface diffusion is an interesting and practically important phenomenon in many areas of chemistry and physics. One emerging problem is that of Li wetting on high-Z plasma-facing metals, especially tungsten, for application in tokamak reactors. We report construction of a Li-W binary force field to describe the interface between liquid Li and solid W. We show that this force field can simulate well the atomic processes of liquid Li diffusing across the W surface, as compared with results from first-principles calculations. We find that Li atoms have different wetting behaviors on different surfaces of W. Diffusion is the fastest on the (110) surface and the slowest on the (100) surface. Diffusion of second Li layer on the (110) surface is activated at relatively low temperatures above 262 K. In addition, the diffusion rate of single-layer Li changes with the coverage rate of Li on (110) surface. High diffusion coefficients at coverage rate of θ = 1/6, 1/3 and 1 are found to be related to the 2D phase transition of Li on the (110) surface.