Periodic DFT investigation on the structure and properties of TNAD crystal

Abstract

Density function theory calculations were performed at the GGA/PW91, GGA/PBE, and LDA/CA-PZ levels to study the structures and properties of the crystalline TNAD (trans-1,4,5,8-tetranitrotetraazadecalin). The relaxed crystal structure compares well with the experimental data. Analysis on the band structures shows that the frontier energy bands are generally quite flat, and the energy gap between the highest occupied crystal orbital and the lowest unoccupied crystal orbital is about 3.4 eV, indicating that the crystal is an electrical insulator. All the atoms of TNAD make up both the lower and the higher energy bands. The projection of density of state demonstrates that the NONO 2 bond is the most reactive region of the material. The lattice energy is predicted to be Ϫ155.13 kJ/mol at the LDA/CA-PZ level, consistent with the previous studies, whereas it is underestimated by the GGA/PW91 (Ϫ70.41 kJ/ mol) and GGA/PBE (Ϫ74.33 kJ/mol). The optical properties under ambient condition were investigated, including dielectric function, absorption coefficient, and reflectivity. The calculated absorption spectra show a number of absorption peaks in the fundamental absorption region, which are believed to be associated with different exciton states. And the reflectivity spectra are mainly composed of four peak structures,