CoSi2合金电子结构和光学性质的理论研究∗

摘要

The electronic structure and optical properties of CoSi2 alloy materials,were calculated by using the first-principles based on the framework of density functional theory (DFT).The calculated results revealed that there was an obvious overlap between the conduction bands and valence bands,which showed the half-metal characteristics.With increase of the U values,the energy levels near the Fermi level were gradually split apart, the conduction and valence band shifted to the high and low energy,respectively.When U value was equal to 8.0 eV,CoSi2 alloy appeared spin-splitting phenomenon.The calculated results of charge density showed that the Co-Si bonds were mainly composed of covalent bond and part of ionic bond,which was a kind of mixed va-lence alloy material.Moreover,the most notable character in the CoSi2 alloy was the charge transmission from Si atoms to Co.The optical absorption spectra showed that the absorption peaks have a blue-shift,and the in-tensity of absorption spectra weakened with the increases of the HubbardU values.These results indicated that CoSi2 alloy was a good thermoelectric material with certain luminescence properties.%采用基于密度泛函理论框架的第一性原理计算方法,利用 LSDA＋U 方法计算了 CoSi2合金材料的电子结构和光学性质。计算结果表明,CoSi2合金能带结构的导带和价带在费米能级附近存在明显的交叠,表现出半金属特性。随着U 值的增加,费米能级处的能级逐渐分裂,导带部分和价带部分分别向高能和低能方向移动,当U＝8时,CoSi2合金出现自旋劈裂现象。电荷密度计算结果显示 Co—Si 键是一种以共价键为主且含有部分离子键成分的混合价合金材料,载流子具有明显的由 Si 原子向 Co 原子的电荷转移特性。光学吸收谱分析表明,随着U 值的增大,Co-Si2材料的吸收峰发生蓝移现象,吸收峰强度逐渐减弱。这些结果表明,CoSi2合金材料是一种很好的具有一定发光性能的热电材料。