DFT study of structural, electronic and vibrational properties of pure (Al 2 O 3 ) n ( n = 9, 10, 12, 15) and Ni-doped (Al 2 O 3 ) n ( n = 9, 10) clusters

The geometrical, electronic and vibrational properties of pure (Al 2 O 3 ) n ( n = 9, 10, 12, 15) clusters and Ni-doped (Al 2 O 3 ) 9–10 clusters are investigated by density functional theory. There are four different Ni-doped (Al 2 O 3 ) 9 clusters and one Ni-doped (Al 2 O 3 ) 10 cluster taken into account. Compared with the pure clusters, the Ni-doped (Al 2 O 3 ) 9–10 clusters have narrower HOMO–LUMO energy gaps. The results indicate that the impurity of Ni atom is mainly responsible for the reduction of the HOMO–LUMO energy gap. One characteristic vibration band at about 1030 cm −1 is found in the vibrational frequencies of the Ni-doped (Al 2 O 3 ) 9–10 clusters, which is caused by the asymmetric Al–O–Al stretching vibration. Another band at around 826 cm −1 involving the characteristic vibration of Ni–O bond is in good agreement with experimental results.