Computational study of TbMn2O5 and Tb2MnCoO6 to probe the structural, vibrational and optoelectronic properties using PBE + U functional

Abstract

The structural, electronic, vibrational and optical properties of TbMn2O5 and Tb2MnCoO6 have been studied by using density functional implemented into CASTEP and GULP codes. The geometry optimization is achieved using PBE-functional in CASTEP code. So far as, the structure is optimized using Buckingham potential through GULP code. The calculated lattice constants for TbMn2O5 and Tb2MnCoO6 are found to be a = 6.973 Å, b = 8.638 Å, c = 6.097 Å and a = 5.559 Å, b = 7.415 Å, c = 5.182 Å, respectively in the orthorhombic phase of these crystal structures. The electronic band structure as well as density of states of both structures unveils that the studied materials belong to semi-metallic family. Force constant matrix related to force field methods is used to calculate the phonons of the studied materials. Phonon dispersion and vibrational density of states (VDOS) are plotted to calculate the vibrational modes. In addition, infrared and Raman spectroscopy have been performed to characterize modes of the vibrations. The calculated modes of vibrations of TbMn2O5 demonstrate an excellent agreement with available experimental results. Finally, the optical behavior of TbMn2O5 and Tb2MnCoO6 has been investigated using Kramer-Kronig relations in terms of dielectric constant, reflectivity, absorption coefficient and refractive index in the frequency range 0–700 cm-1.