GaAs(100) c(4 x 4) surfaces were examined by ab initio calculations, under As-2, H-2 and N-2 gas mixed conditions as a model for GaAs1-xNx, vapor-phase epitaxy (VPE) on GaAs(100). Using a simple model consisting of As-2 and H-2 molecules adsorptions and As/N atom substitutions, it was shown to be possible to examine the crystal growth behavior considering the relative stability of the resulting surfaces against the chemical potential of As-2, H-2 and N-2 gases. Such simple model allows us to draw a picture of the temperature and pressure stability domains for each surfaces that can be linked to specific growth conditions, directly. We found that, using this simple model, it is possible to explain the different Nincorporation regimes observed experimentally at different temperatures, and to predict the transition temperature between these regimes. Additionally, a rational explanation of N-incorporation ratio for each of these regimes is provided. Our model should then lead to a better comprehension and control of the experimental conditions needed to realize a high quality VPE of GaAs1-xNx. (C) 2015 Elsevier B.V. All rights reserved.