Density Functional Calculations of Small Anionic Clusters of Group III Nitrides.

Costales, Aurora; Pandey, Ravindra

doi:10.1002/chin.200311002

Cited by 1 publication

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“…It is projectable that LEDs could perform better, replacing the century-old incandescent bulb, and be used also for efficient power-handling circuitry in hybrid electric vehicles . Materials and devices made from or containing GaN have been extensively studied since the early 90s experimentally and theoretically using ab initio electronic structure methods for GaN clusters. ,,− …”

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confidence: 99%

Ab Initio Analysis and Harmonic Force Fields of Gallium Nitride Nanoclusters

Perez-Angel

Seminario

2011

J. Phys. Chem. C

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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.

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