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Ammonium DiNitramide (ADN) is one of the most promising green energetic oxidizers for future rocket propellant formulations. In the present work, we report a detailed theoretical study on structural, elastic, and vibrational properties of the emerging oxidizer under hydrostatic compression using various dispersion correction methods to capture weak intermolecular (van der Waals and hydrogen bonding) interactions. The calculated ground state lattice parameters, axial compressibilities, and equation of state are in good accord with the available experimental results. Strength of intermolecular interactions has been correlated using the calculated compressibility curves and elastic moduli. Apart from this, we also observe discontinuities in the structural parameters and elastic constants as a function of pressure. Pictorial representation and quantification of intermolecular interactions are described by the 3D Hirshfeld surfaces and 2D finger print maps. In addition, the computed infra-red (IR) spectra at ambient pressure reveal that ADN is found to have more hygroscopic nature over Ammonium Perchlorate (AP) due to the presence of strong hydrogen bonding. Pressure dependent IR spectra show blue- and red-shift of bending and stretching frequencies which leads to weakening and strengthening of the hydrogen bonding below and above 5 GPa, respectively. The abrupt changes in the calculated structural, mechanical, and IR spectra suggest that ADN might undergo a first order structural transformation to a high pressure phase around 5-6 GPa. From the predicted detonation properties, ADN is found to have high and low performance characteristics when compared with ammonium based energetic oxidizers and well-known secondary explosives, respectively., Comment: 28 pages, 11 figures

A systematic computational study on the structural, electronic, bonding, and optical properties of orthorhombic ammonium azide (NH$_4$N$_3$) 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 non-bonded interactions in molecular crystalline NH$_4$N$_3$. The ground state lattice parameters and fractional co-ordinates obtained using the dispersion correction schemes are in excellent agreement with experimental results. We calculated the single crystal elastic constants of NH$_4$N$_3$ 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$_4$N$_3$ 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$_4$N$_3$ is sensitive to ultraviolet (UV) light. Further, we also analyzed the detonation characteristics of the NH$_4$N$_3$ using the reported heat of formation and calculated density. NH$_4$N$_3$ 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., Comment: 6 Figures

High pressure behavior of potassium chlorate (KClO$_3$) has been investigated from 0-10 GPa by means of first principles density functional theory (DFT) calculations. The calculated ground state parameters, transition pressure and phonon frequencies using semiempirical dispersion correction scheme are in excellent agreement with experiment. It is found that KClO$_3$ undergoes a pressure induced first order phase transition with an associated volume collapse of 6.4$\%$ from monoclinic (\emph{P2$_1$/m}) $\rightarrow$ rhombohedral (\emph{R3m}) structure at 2.26 GPa, which is in good accord with experimental observation. However, the transition pressure was found to underestimate (0.11 GPa) and overestimate (3.57 GPa) using LDA and GGA functionals, respectively. Mechanical stability of both the phases are explained from the calculated single crystal elastic constants. In addition, the zone center phonon frequencies have been calculated using density functional perturbation theory at ambient as well as at high pressure and the lattice modes are found to soften under pressure between 0.6 to 1.2 GPa. The present study reveals that the observed structural phase transition leads to changes in the decomposition mechanism of KClO$_3$ which corroborates with the experimental results., Comment: 6 Figures