Structural, electronic and vibrational properties of smallGaxNy (x+y = 2–5) nanoclusters: a B3LYP-DFT study

Abstract

An ab initio study of the stability, structural and electronicproperties has been made for 49 gallium nitride nanoclusters,GaxNy (x+y = 2–5). Among the various configurations corresponding to a fixedx+y = n value, the configuration possessing the maximum value of binding energy (BE) is named asthe most stable structure. The vibrational and optical properties have been investigatedonly for the most stable structures. A B3LYP-DFT/6-311G(3df) method has beenemployed to optimize the geometries of the nanoclusters fully. The binding energies (BEs),highest-occupied and lowest-unoccupied molecular orbital (HOMO–LUMO) gaps and thebond lengths have been obtained for all the clusters. We have considered the zero-pointenergy (ZPE) corrections ignored by the earlier workers. The adiabatic and verticalionization potentials (IPs) and electron affinities (EAs), charge on atoms, dipolemoments, vibrational frequencies, infrared intensities (IR Int.), relative infraredintensities (Rel. IR Int.) and Raman scattering activities have been investigatedfor the most stable structures. The configurations containing the N atoms inmajority are seen to be the most stable structures. The strong N–N bond has animportant role in stabilizing the clusters. For clusters containing one Ga atomand all the others as N atoms, the BE increases monotonically with the numberof the N atoms. The HOMO–LUMO gap and IP fluctuate with the cluster sizen, having larger values for the clusters containing odd number of Natoms. On the other hand, the EA decreases with the cluster size up ton = 3, and shows slow fluctuations thereafter for the larger clusters. In general, the adiabatic IP(EA) is smaller (greater) than the vertical IP (EA) because of the lower energies of themost stable ground state of the cationic (anionic) clusters. The optical absorptionspectrum or electron energy loss spectrum (EELS) is unique for every cluster,and may be used to characterize a specific cluster. All the predicted physicalquantities are in good agreement with the experimental data wherever available.The growth of these most stable structures should be possible in experiments.