Electronic band structure and optical properties of ferroelectric TGS, TGSe and TGFB crystals

Structural and electronic properties of the ferroelectric TGS, TGSe and TGFB crystals were studied by the ab initio method in the framework of the density functional theory. Equation of state (total energy vs. unit cell volume), band structure, density of electronic states and dielectric functions in the range of valence electrons excitations have been calculated using the plane waves and pseudopotentials. The comparable structural and electronic characteristics of TGS, TGSe and TGFB crystals are obtained for the first time and discussed in relation to the reference experimental data. The semiempirical dispersion-correction approach implemented in CASTEP code has been applied to the materials studied and has been shown to produce results more close to the experimental data. Correlation of the total energy difference E-p - E-f for paraelectric and ferroelectric phases and Curie temperatures of the ferroelectric phase transitions has been revealed for TGS, TGSe and TGFB crystals, that was not reported before. (C) 2015 Elsevier B.V. All rights reserved.