Effect of indium on the localized vibrational mode of nitrogen in GaN$_x$As$_{1-x}$

The effect of the substitution of nearest-neighbor gallium atoms by indium (In-N-Ga, In-N-In) on the frequency of the localized vibrational mode of substitutional nitrogen in the dilute nitride, GaN$_x$As$_{1-x}$, has been studied within first-principles density functional theory, using a supercell approach. The splitting of the highly localized triply-degenerate mode into singly- and doubly-degenerate modes is obtained and compared with available Raman and FTIR spectroscopy measurements. The results are in good agreement with the experimental values.