New high-pressure monoclinic phase of Sn

High-pressure structure phase transitions of Sn were studied by using the unbiased CALYPSO structure prediction method combined with first-principles calculations. The experimental structures of Fd-3m, I41/amd, I4/mmm, Immm, Im-3m and P63/mmc were successfully reproduced in our crystal structure searches. Furthermore, we firstly uncovered a novel high-pressure structure of Sn with space group P21/m symmetry stabilized at the pressure range of 6.1–21.5 GPa. The results of elastic constants and phonon dispersion curves show that the P21/m structure is dynamically and mechanically stable at the considered pressures. Atomic structure of the P21/m phase was very similar to that of I4/mmm (body-centered tetragonal) under the same pressure. Our findings enrich the high pressure phases of Sn and lay the foundation for further theoretical and experimental research.