First principles analysis of the terahertz spectrum of PETN

This paper focuses on the establishment of methodologies for the successful application of first principles theoretical analyses in the understanding of the terahertz spectroscopy of molecular solids, particularly high-energy materials. A solid-state density functional theoretical study has been performed on the high explosive pentaerythritol tetranitrate (PETN) in order to address the relationships between the choice of computational parameters and the predictions of molecular and solid-state properties, such as molecular geometries, intermolecular interactions within the crystal cell, charge distributions, and solid-state vibrations in the terahertz (3 to 200 cm ^-1) region. This investigation has lead to the conclusion that the BP functional has the best overall performance and the choice of basis set is the most critical theoretical variable. Varying other parameters such as grid size, orbital cut-off, and convergence criteria lead to negligible differences among the calculations.