Structural, elastic, vibrational and optical properties of energetic material octanitrocubane studied from first-principles theory.

We present a thorough density functional theory based computational study of crystalline properties of cubane caged potential energetic material octanitrocubane (ONC). As expected for a layered molecular solid, van der Waals corrections are inevitable and the same has been incorporated to capture the ground state properties more accurately. Study of Born effective charge and zone centered phonon frequencies using density functional perturbation theory reveals the important role of N2, N4 type nitrogen and associated oxygen atoms in contributing to the high intensity infrared modes. From the calculated electronic band structure we can conclude that ONC is an insulator with a band gap of 5.31 eV. The optical properties of ONC are found to be nearly isotropic in low energy region in spite of strong anisotropic crystal structure.