Never ending saga of a simple boundary

The structure and associated translational states of the Σ=3(112) symmetrical tilt grain boundary in niobium and molybdenum are investigated theoretically by three distinct computational methods. The results are compared with those of previous theoretical studies as well as with transmission electron microscopy observations. It was found that for this grain boundary, when fully relaxed, two possible translation states - ''reflection'' and ''sheared'' - are energetically almost degenerate in the two transition metals studied and thus comparison with experiments is ambivalent. This prevents the Σ=3(112) boundary from being a suitable benchmark for validations of semi-empirical theoretical models of interatomic interactions. (orig.)