含羟基结构熔石英光电性质的第一性原理研究

First principles study of the electronic and optical properties of silica glass with hydroxyl group

熔石英是高功率激光装置中广泛使用的激光透镜材料,采用第一性原理结合平面波赝势方法,研究了熔石英材料中羟基结构的生成模式,系统计算了材料的电子态密度、差分电荷密度、原子电荷布居分布,分析了包含羟基熔石英材料的光学跃迁模式,研究结果表明:熔石英中的三配位硅原子缺陷在禁带中生成了两条缺陷能级,分别位于7.8和8.8 eV;研究还发现氢原子与五配位硅原子发生相互作用生成羟基结构,该反应还使三配位硅原子的杂化方式由sp^2变为sp^3,这种羟基结构会影响体系的电子结构,使原有的7.8和8.8ev缺陷能级消失,并在费米面上生成一条半占据态缺陷能级,引起激发能为6.2 eV的光学跃迁。

The formation model of hydroxyl group in silica glass is studied by first-principles calculations combined with coupling plane wave pseudo-potential method. The electronic structures and optical properties of silica glass with and without hydroxyl group are systematically calculated, including electronic densities of states, charge difference densities, Bader charge, etc. And optical transition models are analyzed. Our results show that three-fold coordinated silicon in silica glass induces two defect energy levels in forbidden gap, which are at 7.8 eV and 8.8 eV, respectively. Also, we find that H atom can interact with five-fold coordinated Si and forms hydroxyl group, and causes the three-fold coordinated silicon atom to change from sp2 hybridization to sp3 hybridization. Such a kind of hydroxyl group influences the electronic structure and optical properties of silica glass, by forming a half-occupied electronic state at Fermi level, and also by generating an optical transition, of which the excitation energy is 6.2 eV.