Structure transformation and electronic properties of m-aminobenzoic acid under different pressures

In this paper, the structural, electronic and optical absorption properties of m-aminobenzoic acid crystals (hereinafter referred to as m-amino) in the pressure range of 0-300 GPa are calculated by density functional theory (DFT). The changing trend of the lattice constant of m-amino under different pressures is analyzed. We find that the crystal undergoes complex transformation. Furthermore, it can be seen that the structure of m-amino along the b-axis is stiffer than that along the a-axis and c-axis, suggesting that the crystal has anisotropic compressibility. Through the analysis of the band gap and density of states of m-amino, it is found that the electronic properties of m-amino are transformed from semiconductor phase to metal phase at 100 GPa, then jump into the semiconductor phase and maintain the metal phase again in the pressure range of 150-250 GPa. Repeated phase transitions indicate that the structure of m-amino becomes more unstable as the pressure increases. Besides, from the absorption spectra, the optical activity of rn-amino is relatively high with the increase of pressure, and two obvious structural transitions are observed at 70 and 270 GPa, respectively.