Abstract : The failure of bands alignment models to predict bands alignment in MOS stack (metal-oxide-semiconductor) make it useful and interesting an atomistic study. We show two ab initio theories: Firstly the density functional theory of which depend the Abinit and Siesta codes used to study the quantum nature of materials; then the GW approximation theory which correct electronic energy levels badly assessed with the approximation used in DFT computation. These two theories are applied to each material compounding the stack. Then we study how the dipole interferes with the bands alignment. Thanks to the GW approximation, the Van de Walle and Martin method is retrofit to evaluate precisely these bands alignment. Finally this method is applied to several oxide/semiconductor and metal/oxide interfaces and shows that the band alignment computed are in good agreement with experimental measurements.