  While being of persistent interest for the integration of lattice-matched
laser devices with silicon circuits, the electronic structure of dilute nitride
III/V-semiconductors has presented a challenge to ab initio computational
approaches. The root of this lies in the strong distortion N atoms exert on
most host materials. Here, we resolve these issues by combining density
functional theory calculations based on the meta-GGA functional presented by
Tran and Blaha (TB09) with a supercell approach for the dilute nitride Ga(NAs).
Exploring the requirements posed to supercells, we show that the distortion
field of a single N atom must be allowed to decrease so far, that it does not
overlap with its periodic images. This also prevents spurious electronic
interactions between translational symmetric atoms, allowing to compute band
gaps in very good agreement with experimentally derived reference values. These
results open up the field of dilute nitride compound semiconductors to
predictive ab initio calculations.
