Ab initio study of the electronic, elastic, vibrational and dielectric properties of KBaBi

Abstract

KBaBi is predicted to be a topological insulator recently, but most fundamental properties of it have not been studied. In this work, first-principles calculations were carried out to study its electronic, bonding, elastic, vibrational and dielectric properties. The results indicate that KBaBi has a band gap of 0.22 eV with the presence of spin orbital coupling. Weak p-d hybridization exists between the Ba 5d and the Bi 6p orbitals, so KBaBi has some covalent property, as revealed by the electron density difference. Studies imply that KBaBi is mechanically and dynamically stable, but it is mechanically anisotropic. KBaBi has a theoretical bulk modulus of 20.8 GPa and a shear modulus of 11.7 GPa. Group theory analysis indicates that there are six infrared- and four Raman-active modes at the Brillouin zone center of KBaBi. The vibrational frequencies and the corresponding eigenvectors were calculated and discussed. Calculation unveils that the electrons have more dielectric contribution to the total dielectric constants than the ions in the ab plane, but it is revised along the c axis. Investigations of the band structure, the Debye temperature and the phonon dispersion curves indicate that KBaBi is a promising thermalelectric material.