Bulk h-BN belongs to centrosymmetric space group P6 3 /mmc, which consists of planer h-BN monolayers (AA' stacking i.e. one h-BN monolayer is 180 °rotated with respect to the next layer). Our calculated lattice parameters of h-BN (a = b = 2.509Å and c = 6.730Å) with van der Waals interactions are in good agreement with the experimental values (a = b = 2.504Å ∂η 3 is calculated using finite difference method, where ∆P = P3(η3) -P3(η3 = 0) is the polarization change along c-direction obtained from Berry phase calculation in response to applied strain (η3) along c-direction. To calculate total e33, we relax both ions and electron charge distribution in response to η3, whereas ions are kept fixed at their unstrained positions to obtain the electronic part of e33. and c = 6.660Å) . We find that AA' stacking is 9.055 meV/atom lower in energy than AB type stacking (where N atoms of the layers are on top of each other, but B lie at the centre of the hexagon) for bulk h-BN. Therefore, we choose AA' stacking for further investigation. We also confirm that flat h-BN is 43.377 meV/atom lower in energy than its hypothetical wurtzite structure. On the other hand, both bulk w -AlN and w -GaN have non-centrosymmetric wurtzite structure (space group: P6 3 mc), where AlN or GaN layers are AA' stacked, but the layers are buckled along the c-direction. Our computer lattice parametersw -AlN: a = b = 3.129 Å and c = 5.015 Å; w -GaN: a = b = 3.246 Å and c = 5.276 Åwithout van der Waals interaction, as the layers are covalently bonded, are also consistent with the experimental values (a = 3.110Å, c = 4.980Å for AlN and a = 3.190Å, c = 5.189 Å for GaN) .