Relaxation and electronic structure of the V2O3(0001) surface: ab initio cluster model studies

The electronic structure and geometric relaxation of the (0001) surface of rhombohedral vanadium sesquioxide, V2O3, is studied theoretically with large surface cluster models where ab initio density functional theory is used to characterize charging and bonding. Geometric relaxation in the topmost surface region, up to 5 layers, with its three different bulk terminations is determined by minimizing total energies of the clusters. This yields major relaxation effects depending on the termination. The oxygen layer termination OVV′ exhibits strong relaxation of sub-surface vanadium layers resulting in increased ionic charging at the surface (measured by corresponding atom charges). The metal layer termination VV′O leads to inwards relaxation of the two topmost vanadium layers by over 40% resulting also in increased surface charging. Ionic charging at the surface is the smallest for the half metal layer V′OV termination where only the topmost vanadium layer relaxes inwards by 30% in addition to some rearrangement of sub-surface vanadium. This termination is believed to be the most stable of the three relaxed bulk-type terminations based also on analogies with experiments for Cr2O3(0001). However, total density-of-states and atom-projected partial densities-of-states curves depend relatively little on surface termination to allow a clear discrimination which could assist an unambiguous experimental identification.