Electronic structure of zinc blende AlN(1-x)$Px alloy has been calculatedfrom first principles. Structural optimisation has been performed within theframework of LDA and the band-gaps calculated with the modified Becke-Jonson(MBJLDA) method. Two approaches have been examined: the virtual crystalapproximation (VCA) and the supercell-based calculations (SC). The compositiondependence of the lattice parameter obtained from the SC obeys Vegard's lawwhereas the volume optimisation in the VCA leads to an anomalous bowing of thelattice constant. A strong correlation between the band-gaps and the structuralparameter in the VCA method has been observed. On the other hand, in the SCmethod the supercell size and atoms arrangement (clustered vs. uniform) appearto have a great influence on the computed band-gaps. In particular, ananomalously big band-gap bowing has been found in the case of a clusteredconfiguration with relaxed geometry. Based on the performed tests and obtainedresults some general features of MBJLDA are discussed and its performance forsimilar systems predicted.
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