Computational Study of Solid Energetic Oxidizer Ammonium Nitrate under High Pressure

Understanding the crystal structure, bonding and stability are crucial to explore the potential applications of an energetic material. In the present work, we made a detailed analysis of crystal structure, hydrogen bonding, equation of state and vibrational spectra of AN-IV using van der Waals density functional calculations. The obtained ground state properties are in good agreement with the experimental data. The calculated elastic moduli show that the AN-IV is mechanically stable. The computed elastic and equilibrium bulk moduli indicate the soft nature of this material. We have also calculated the zone center phonon frequencies. The crystal structure of AN-IV with Pmmn symmetry is found to be dynamically unstable at the center of the Brillouin zone within the harmonic approximation. Our calculations suggest that anharmonic effects play a major role in determining the stability of the energetic material under investigation.