Ab Initio Analysis and Harmonic Force Fields of Gallium Nitride Nanoclusters

Abstract

Gallium nitride (GaN) clusters are analyzed to set approaches for more extended calculations at the nanoscale. We test the atom components and very small clusters using the most sophisticated compound methods such as G1ÀG3, CBS, W1, and a flavor of DFT (B3PW91) using several sizes and qualities of basis sets. Results are compared with very precise experimental information when available. Interestingly, the B3PW91 yields results comparable to the high-quality compound methods. For negative ions, it is difficult to assess the quality of the methods; the electron affinity (EA) calculations, as expected, yield better results when diffuse functions are used. All ionization potentials (IPs) are well reproduced by all methods, but the best results are obtained with B3PW91 for the Ga atom and with the compound methods for N. Among the compound methods, the W1 ones use the largest basis sets with 93 functions (which include two sets of g-functions) for one gallium atom. Geometry optimizations are performed with MP2 for the G-methods, HF for the CBS-methods (except QB3), and B3LYP for the CBS-QB3 and all W1 methods. G3 followed by B3PW91 yields the best result for the Ga quartet excited state, and there is little difference for the excited doublet of N, among the compound methods. In general all calculated IPs and EAs are in good agreement with existing experimental data. We also performed extended calculations of bigger GaN clusters such as Ga x N y where 6 < x ≈ y < 19 using B3PW91/6-311G(d). Finally, we calculate second derivative and thus the vibrational spectra for all clusters studied. We generate harmonic force fields using the procedure Fuerza and averaged the force field parameters and use them in a simple heating molecular dynamics calculation that yields an acceptable value for the heat capacity.

Adsorption of gas molecules on a graphitic GaN sheet and its implications for molecule sensors

“…40 Meanwhile, the corresponding adsorbate distance of Ga-N bond between the N atom in NH 3 and the Ga atom in sheet is 2.19Å, which is a little larger than the Ga-N bond lengths in the PL-GaN sheet, but similar to the Ga-N bond lengths in the small GaN clusters 36,37,[41][42][43] and nonpolar GaN surface. 44 These results indicate that NH 3 molecule is chemisorbed on the PL-GaN sheet.…”

Electronic structure of a hydrogenated gallium nitride nanoparticle

“…As can be seen, the geometrical structure of the GaN:H nanoparticle is very similar to that of the crystal structure of GaN. In addition, the fact of no observed differences in a nanostructure compared to the crystal cannot be attributed to the DFT/B3LYP/LANL2DZ‐ECP methodology employed here, since geometry optimizations of GaN nanoclusters with more sophisticated methodologies also indicate that DFT calculations give the best results .…”

“…It was chosen a nanoparticle with a structure so that the surface of the planes (0001) were well represented, since these surfaces play an important role in the growth of GaN films and nanowires . According to a first principles study on vibrational properties, the smallest particle that appears to have a wurtzite structure is a Ga 19 N 19 cluster . The size of this cluster was enlarged just enough to have three planes along the c axis, [0001] direction.…”

Polarisable multipolar electrostatics from the machine learning method Kriging: an application to alanine

“…Molecular dynamics and mechanics methods are used to investigate a wide variety of chemical problems, including but not limited to peptide structure [1], semiconductors [2] and the origins of life [3]. There is a competition between the accuracy of the results of such studies and the computational cost of carrying them out.…”