Mg-Ti-H体系电子结构与光学性质的第一性原理计算

First-Principles Calculation of Electronic Structures and Optical Properties of Mg-Ti-H System

摘要:

采用基于密度泛函理论的第一性原理赝势平面波方法，对不同Ti含量的MgxTi(1-x)H2 (x=0.25, 0.5, 0.75, 0.875)体系的电子结构进行研究，并预测其光学性质。电子态密度计算结果表明：在MgH2中加入Ti原子，使MgxTi(1-x)H2体系呈现金属特性，这源于Ti诱导费米能级处电子密度增加和费米能级附近能隙消失。电荷密度分析进一步得到了Ti-H原子间形成比Mg–H原子间更强的共价键的成键本质。光学性质预测结果表明，MgxTi(1-x)H2体系中Ti含量对其可见光能量附近的光学性质存在重要影响，较低Ti含量（如Mg0.875Ti0.125H2）不利于提高其可见光的吸收能力，而较高Ti含量（如Mg0.25Ti0.75H2）则对可见光的反射较高。计算结果为制备具有优良的太阳光吸收能力和光电转化效率的Mg-Ti-H光电材料提供了理论依据。

Abstract:

The first-principles calculations were performed to investigate the electronic structure and the optical properties of the MgxTi(1-x)H2 (x = 0.25, 0.5, 0.75, 0.875) systems with different Ti contents by the pseudopotential plane-wave method based on density functional theory. The electronic densities of state reveal that the MgxTi(1-x)H2 hydrides exhibit metallic characteristics by adding Ti atom to MgH2 hydride. It originates from the increasing of the valence electrons at Fermi level and the vanishing of band gap near Fermi level. The bonding nature of the hydrides was investigated by analyzing the charge distribution of MgxTi(1-x)H2, and it shows stronger covalent bonding between Ti and H than between Mg and H. The calculated results from the optical properties of MgxTi(1-x)H2 show that Ti content in MgxTi(1-x)H2 systems has an important influence on the optical properties near visible light energy region. For the lower Ti content in MgxTi(1-x)H2 such as x=0.875, it is not favorable to improve absorption over the whole visible region. Whereas the reflection is high for the higher Ti content, such as x=0.25. The calculated results provide a theoretical basis for preparing Mg-Ti-H photoelectric materials with excellent absorption and photoelectric conversion efficiency over the whole visible region.