Mg$_{2}$Sn stannide under pressure: first-principles evolutionary search results

First-principles Density Functional Theory (DFT) evolutionary searches were carried out for magnesium stannide Mg$_{2}$Sn structures. The well-known hexagonal structure of $P63/mmc$ symmetry is shown to transform to orthorhombic Pmmm structure under pressure $Р\sim$ 5.1 GPa. The last one is stable up to pressures $Р\sim$ 250 GPa. It can exist together with orthorhombic $Cmmm$ structure.