LAUSR

Abstract Structural, electronic and optical properties of quasi-one-dimensional material BaTiSe 3 were investigated using density functional theory and were compared with that of BaTiS 3 , which is well known for exhibiting the highest broadband giant birefringence. The relative stability of two different structures of BaTiS 3 , one crystallizing in the space group P 6 3 / mmc and another in P 6 3 mc were studied using PBE exchange-correlation functional. It was found that the recently synthesized P 6 3 mc structure is more stable than the P 6 3 / mmc structure. Electronic structure calculations with HSE06 and DFT+U methods predicted that both BaTiS 3 and BaTiSe 3 are narrow band gap semiconductors. These calculations also showed that BaTiS 3 is a direct band gap semiconductor while BaTiSe 3 is an indirect band gap semiconductor. Calculations of optical properties using the DFT+U method for different U values showed that both materials exhibit high optical anisotropy. Birefringence of both materials were calculated and compared with experimental results of BaTiS 3 . It was found that BaTiSe 3 exhibits broadband giant birefringence at least of the order of that exhibited by BaTiS 3 .