DFT study of structural, electronic and vibrational properties of pure (Al2O3)n (n = 9, 10, 12, 15) and Ni-doped (Al2O3)n (n = 9, 10) clusters

► We investigate the geometrical structures and stability of Ni-doped (Al2O3)n (n = 9, 10) clusters. ► The impurity of nickel atom is mainly responsible for the reduction of the energy gap. ► The vibrational band at 1030 cm−1 is ascribed to the asymmetric Al-O-Al stretching vibration.