The embedded-atom model applied to vacancy formation in bulk aluminium andlithium

The embedded-atom model (EAM) is applied to the study of vacancy formation in bulk aluminium and lithium. A systematic study is undertaken into the se nsitivity of the EAM potentials and embedding energy functionals as a funct ion of the unrelaxed vacancy formation energy which is normally obtained vi a ab initio density functional calculations. The effect of this 'empirical' input parameter on the vacancy relaxation energy, formation volume and str uctural relaxation is also investigated using super-cell sizes not normally accessible in orbital-based ab initio relaxation studies. We find that for aluminium, for which at most a fifth-nearest-neighbour model is required, the vacancy relaxation energy and formation volume are not sensitive functi ons of the unrelaxed vacancy formation energy. For lithium, for which at le ast a ninth-nearest-neighbour model is needed, the situation is somewhat di fferent: both the vacancy relaxation energy and the formation volume are fo und to be a noticeably related to the unrelaxed vacancy formation energy. F or both solids, the structural relaxation was found to be largely insensiti ve to the unrelaxed vacancy formation energy, agreeing well with previous a b initio calculations. In particular for aluminium, the EAM result agrees e xtremely well with recent orbital-free density functional calculations whic h use super-cell sizes approaching those used here. Finally, we find that f or lithium, the embedding energy functional has negligible curvature for a wide range of local electronic densities, justifying the use of a simpler p air potential description for lithium in mildly inhomogeneous systems.