Computational study of structural, electronic, and optical properties of crystalline NH < inf > 4 < /inf > N < inf > 3 < /inf >

Abstract

A systematic computational study on the structural, electronic, bonding, and optical properties of orthorhombic ammonium azide (NH 4N 3) has been performed using planewave pseudopotential (PW-PP) method based on density functional theory (DFT). Semiempirical dispersion correction schemes have been used to account for nonbonded interactions in molecular crystalline NH 4N 3. The ground state lattice parameters, and fractional coordinates obtained using the dispersion correction schemes are in excellent agreement with experimental results. We calculated the single crystal elastic constants of NH 4N 3, and its sensitivity is interpreted through the observed ordering of the elastic constants (C 33 > C 11 > C 22). The electronic structure and optical properties were calculated using full potential linearized augmented plane wave (FP-LAPW) approach with recently developed functional of Tran-Blaha modified Becke-Johnson (TB-mBJ) potential. The TB-mBJ electronic structure shows that NH 4N 3 is a direct band gap insulator with a band gap of 5.08 eV, while the calculated band gap with standard generalized gradient approximation is found to be 4.10 eV. The optical anisotropy is analyzed through the calculated optical constants, namely, dielectric function and refractive index along three different crystallographic axes. The absorption spectra reveal that NH 4N 3 is sensitive to ultraviolet (UV) light. Further, we also analyzed the detonation characteristics of the NH 4N 3 using the reported heat of formation and calculated density. NH 4N 3 is found to have a detonation velocity of 6.45 km/s and a detonation pressure about 15.16 GPa computed by Kamlet-Jacobs empirical equations. © 2012 American Chemical Society.