DFT study of pressure effects in molecular crystal 4,10-dinitro-2,6,8,12-tetraoxa- 4,10-diazatetracyclo-[5.5.0.0^5,90^3,11]-dodecane

Density functional theory was used to study the structural, electronic, and optical properties of crystalline 4,10-dinitro-2,6,8,12-tetraoxa- 4,10-diazatetracyclo-[5.5.0.0^5,90^3,11]-dodecane (TEX) under hydrostatic pressure. The results indicate that there is a displacive transition in TEX under compression that has never been found in experiments. As the pressure increases, the band gap gradually decreases but presents an abnormal increase at 61 GPa, called the structural transition; moreover, the gap reduction is more pronounced in the low-pressure range compared with the high-pressure range. An analysis of density of states shows that the electronic delocalization in TEX is enhanced gradually under the influence of pressure. The peaks of the imaginary parts of the dielectric functions, energy-loss function, and reflectivity may come mainly from the electron transitions between the oxygen 2p and nitrogen 2p states. The electron energy-loss function presents a blue shift under compression. TEX has relatively higher optical activity at high pressure than at ambient conditions. (author)