Molecular dynamics simulations of self-diffusion of adatoms on tungsten surfaces

Abstract

Under an extreme fusion environment, the self-diffusion behaviors of W adatoms on W surfaces are thought to have a very important influence on the modification of surface morphology of W. Thus, in the present paper, the self-diffusion behaviors of W adatom clusters on the three typical W surfaces ((0 0 1), (0 1 1) and (1 1 1)) were investigated using the parallel replica dynamics method and the conventional molecular dynamics method. The diffusion barrier was obtained by the nudged elastic band method, and the corresponding pre-factor was also calculated. The results show that adatom clusters on the (0 1 1) surface are easier to diffuse than those on the (0 0 1) surface, and the diffusion barriers of single adatoms are 0.46 eV and 1.61 eV, separately. Furthermore, for the clusters of different sizes on the (0 0 1) surface, all diffusion barriers are strongly affected by relative positions between the jump adatom and its neighboring adatoms, but little by farther adatoms; all the scales of the pre-factors are fs−1. However, on the (0 1 1) surface, the energy barrier is mainly determined by the whole structure of an adatom cluster, the diffusion pathways are much more complex, and even trimer-shearing may occur, while all the scales of the pre-factors are ns−1. On the (1 1 1) surface, surface atoms can move and cause surface undulation, the adatoms and substrate atoms are indistinguishable, so it is meaningless to just obtain diffusions of the adatoms. This work can direct the investigation of the adatom diffusion on W surfaces by larger simulation methods, such as kinetic Monte Carlo.