Ab initio calculations of rigid-body displacements at the S5 „210... tilt grain boundary in TiO2

Through extensive ab initio total energy calculations of the S5 ~210! grain boundary in TiO2 ~rutile!, the remarkably large rigid-body contractions found by high resolution electron microscopy and Z-contrast imaging are explored. Unlike previous calculations, this work emphasizes the importance of the displacements of the two halves of the bicrystal towards one another. Previous experimental work suggests that the stochiometry and ionic charges at the boundary are preserved at their bulk values and therefore vacancies and impurities within the grain boundary core were not considered. The calculations predict no significant rigid-body contraction or expansion. The implications of this result for both computational and experimental studies of rigid-body displacements at grain boundaries are discussed.