  Biaxial strain in coherent epitaxial thin films can have a pronounced effect
on the point defect profile in the film material. Detailed fundamental
knowledge of the interaction of strain with point defects is crucial in
understanding the stoichiometry and resulting properties of strained thin
films. Here we investigate the effect of biaxial strain on the formation energy
of cation and anion vacancies using MnO as a model system. Our density
functional theory calculations show that, as expected from local volume
arguments, compressive strain favours the formation of cation vacancies.
Interestingly, we find that small compressive and tensile strains lead to
ordering of the resulting holes along the in-plane and normal direction
respectively, which should manifest in different anisotropic properties in the
two strain states.
