Why is BeGeN${}_2$ different? A computational bonding analysis

Until recently, all known ordered II-IV-N2 materials crystallised in the $\beta$-NaFeO${}_2$-type in space group Pna2${}_1$. BeGeN${}_2$, however, crystallises in space group Pmc2${}_1$, with a different cation ordering motif long anticipated for this materials class. Chemical bonding analysis is used to rationalise this particular behaviour.