Structural complexity in grain boundaries with covalent bonding

Abstract

The structural properties of two short-period twist boundaries in germanium are explored using a state-of-the-art total-energy calculation. The structures of these boundaries are found to be very complex, with boundary bonds that are distorted and weak. These systems are found to exhibit a large degeneracy in the number of local energy minima. Thus the boundaries have difficulty in arriving at a locally ordered state. The situation may be unique to the semiconducting twist grain boundaries due to the inherent frustration present between the tendency to form directional bonds and the imposed twist geometry which makes the bond formation improbable. This study focuses on the energy, coordination, volume change, and electronic states characteristic of the local minima. A trend towards dimerization is found especially in the highest-angle twist boundary.