Periodic density functional theory study of the high-pressure behavior of crystalline L-serine-L-ascorbic acid.

A detailed study of the structural, electronic and absorption properties of crystalline L-serine-L-ascorbic acid (SAA) in the pressure range of 0-300 GPa was performed by density-functional theory (DFT) calculations in this work. Our results show that the compressible crystal of SAA is anisotropic. Furthermore, specific analysis of the variation tendencies of bond lengths and bond angles under different pressures show that the main structural transformations occur at pressures of 40, 50, 70, 100, 130 and 150 GPa, accompanied by repeated formations and disconnections of covalent bonds between O2(P1) and C2(P2) as well as C3(P1) and O1(P2), and a newly formed five-atom ring at 100 GPa. In addition, from 40 to 230 GPa, complex hydrogen bond transformations occur in SAA under compression, while from 240 to 300 GPa, the curve of lattice constants, bond lengths and bond angles of SAA barely changes, suggesting structural stability after 230 GPa. Then, by analyzing the band gap and density of states of SAA, it was found that the crystal undergoes a phase transformation from insulator to semiconductor at 150 GPa and it becomes more sensitive under compression. In addition, a relatively high optical activity with the pressure increases of SAA was seen from the absorption spectra, and two obvious changes of absorption coefficients were also observed at 50 GPa and 130 GPa, respectively, indicating that structural transformations occur here. Graphical abstract Structural formation and breaking of the five-atom ring O1(P2)-C2(P2)-O2(P1)-C2(P1)-C3(P1) with increasing pressure.