Ab-initio Studies On The Electronic Structures And Optical Properties Of CuCr₂X₄（X=S,Se,Te）

In this paper, we study the electronic structures, magnetic and optical properties of the copper-chromiun spinels CuCr2X4 (X=S, Se, Te) by using the first principle calculation method, which is based on density functional theory.The experimental data was originally used to run the self-consistent calculation, and the deviation between the calculation results and the experimental data was in the range of 1%-3%. CuCr2X4 compounds have identical crystal structure, which lead to a high degree of similarity of their electronic structures and magnetic properties. The occupied part of the band structure can be subdivided into two regions separated by an energy gap of about 6eV.In order to calculate the magnetic properties of CuCr2X4 compounds,VASP and FPLO are both put to use, and obviously in good agreement with experimental result. The magnetism of each primitive cell of CuCr2X4 compounds is 5.013μB(CuCr2S4), 5.101μB(CuCr2Se4),5.337μB(CuCr2Te) respectively. The magnetism of the compound mainly comes from the Cr atoms, which each contributes, respectively, 2.624μB(CuCr2S4),2.755μB(CuCr2Se4),2.853μB (CuCr2Te). The magnetism of Cu and S site is very small. Meanwhile, we calculated the number of electrons in compounds and the results shows that the number of electrons on each atom is not an integer which is different from previous predictions.The optical properties of CuCr2X4 are quite different between each other. We calculated optical conductivity, optical reflection and electron energy loss function for CuCr2X4. We also got their Drude plasma frequency, CuCr2S4 (1.47eV), CuCr2Se4 (1.32eV), CuCr2Te4 (2.66eV). For CuCr2Se4 compound, we compared these three properties with experiment results, which have a good accordance to the calculations. By contrast with the results of non-soc effect, We have verified that the SOC effect has an important impact on optical properties of CuCr2Te4 compounds.