Tin monoxide: Structural prediction from first principles calculations with van der Waals corrections

Tin monoxide is a technologically important p-type material which has a layered structure dictated by nonbonded dispersion forces. As standard density functional theory (DFT) approaches are unable to account for dispersion forces properly, they routinely give rise to a poor description of the unit cell structure. This study therefore applies two forms of empirical dispersion corrections, using either atomic- or ionic-based parameters for the dispersion coefficients, to assess their ability to correctly model the atomic structure and the formation energies of the important p-type defects. Although both approaches show an improvement in the predicted unit cell structure over that with no dispersion corrections, the ionic-based parameter set shows significantly better results, with lattice vectors reproduced within 0.2% of experiment. The atomic-based parameters still predict a distorted cell though, which is carried through to the defective system. On the introduction of defects, a similar degree of structural relaxation is observed regardless of the approach. The defect formation energies, however, are seen to differ more substantially, with the atomic-based set giving an overestimation of the energies due to excessive Sn-Sn interactions. Overall, this study shows that empirical van der Waals corrections utilizing an ionic-based parameter set can be used to model SnO.