Structure, mechanical and phonon stability of the Th-Sn system from ab initio

Abstract

The first-principles projector augmented-wave (PAW) method within the framework of density functional theory (DFT) is applied to study the equilibrium lattice parameters, mechanical stability, tensile and shear properties, lattice dynamical stability and vibration modes of the Th-Sn system. The optimized equilibrium lattice parameters and equilibrium cell volume reproduce perfectly the available experimental data. The individual elastic constants and polycrystalline aggregates of Pm-3m-ThSn3, Cmcm-ThSn2, P63/mcm-Th5Sn3, and P63/mcm-Th5Sn4 have been obtained, the results show that four Th-Sn systems are mechanically stable according to the elastic stability criteria, also, the calculated elastic constants have allowed us to evaluate their elastic anisotropy. Additionally, the Density Functional Perturbation Theory (DFPT) is used to determine the lattice dynamical stability and phonon modes of the series of the Th-Sn compounds, by the vibrational frequencies, it is predicted that four Th-Sn systems are also dynamically stable. Pm-3m-ThSn3 is mechanical and dynamical stable up to 35GPa. The microscopic symmetry properties for optical modes at the center of the Brillouin zone of ThSn3, ThSn2, Th5Sn3, and Th5Sn4 have also been estimated by using group theory.