•The crystal structure of b 2-(acetoxy group) benzoic acid has complicated variations under high pressure.•With the increase of pressure, the optical activity of 2 - (acetoxy group) benzoic acid is ...relatively high.•Electronic character transforms occurs at 270GPa and 280GPa into a metallic system.
Based on Density Functional Theory (DFT), a first-principles study was conducted on the crystal structure, electronic structure, and optical properties of the organic material 2-(acetoxy group) benzoic acid crystal (C9H8O4) under extremely high pressure ranging from 0 to 300GPa. The structure study revealed the significant bonding and bond breaking phenomena at pressures of 80GPa and 270GPa, respectively, indicating that it may induced the lattice phase transitions. The energy band analysis demonstrated that the crystal underwent a transition from a direct bandgap semiconductor at 0GPa to an indirect bandgap semiconductor at 80GPa, and then at 270GPa, the crystal exhibited a metallic phase with a bandgap of 0. The density of states (DOS) provided evidence that this crystal undergo intricate phase transitions under extremely high pressure. The optical properties were further compared and analyzed. It was observed that the peak of optical absorption shifted towards higher energy regions, while the peak of photoconductivity and Loss function shifted towards the blue shift. These findings indicate that extremely high pressures can effectively modulate the structure and properties of C9H8O4 material. This research offers valuable insights for further exploration of the properties of C9H8O4 materials and their potential applications in organic optoelectronic devices.
At present, supercritical technologies use fluids (for example, CO
2
, H
2
O) at temperatures and pressures close to critical. It is not currently clear how important critical fluctuations are for ...dissolution processes and chemical reactions in supercritical fluids. At the same time, our recent work has shown that qualitative changes in the system behavior occurred also at temperatures and pressures much higher than critical. This paper briefly summarizes the latest results of the search and study of the parameters
P
and
T
of the changes of dynamic types in supercritical fluids. It turned out that this region of parameters corresponded to a narrow band, namely, the “Frenkel line.” Reaching this line with increasing temperature corresponds to the disappearance of shear excitations in the liquid at all frequencies. The Frenkel line can be considered as a boundary between the liquid and the dense gas at extremely high pressures far from the critical point. Recently, a simple and mathematically rigorous method for finding the Frenkel line was proposed based on analysis of the autocorrelation function of particle velocities. We suggest using the data of the Frenkel line parameters for actual fluids to move supercritical technologies into the region of extremely high pressures exceeding critical ones by tens and hundreds of times.
