GaN wurtzite nanocrystals approached using wurtzoids structures and their use as a hydrogen sensor: A DFT study

•Bare and H passivated GaN nanocrystals wurtzite structure using wurtzoids.•Vibrational spectra, reduced masses, cohesive energy, bond lengths & angles.•Hydrogen sensing of wurtzite GaN nanocrystals.•Size-dependent nanocrystals Raman, IR.

Wurtzite nanocrystals of gallium nitride are approached using wurtzoid molecular building blocks. Structural and vibrational properties are investigated for both bare and hydrogen passivated GaN molecules and small nanocrystals. Wurtzoids are bundles of capped (3, 0) nanotubes that form the wurtzite phase when they reach nanocrystal or bulk sizes. Results show that experimental bulk gap is generally confined between bare and H passivated wurtzoids. Structural parameters such as bond lengths and bond angles are in good agreement with experimental bulk values. Results of longitudinal optical (LO) vibrational frequencies of present molecules are red shifted with respect to experimental bulk in agreement with previous studies for other materials. Presently modeled GaN wurtzite nanocrystals and molecules are found suitable for the description of hydrogen sensing in ambient conditions in agreement with experimental findings. N sites in GaN wurtzoid are found responsible for the detection of hydrogen molecules. The Ga sites are found to be either oxidized or permanently connected via van der Waals' forces to nitrogen or hydrogen molecules.