锐钛矿相TiO_2光学性质的计算

Calculations of Optical Properties in Anatase TiO_2

TiO2具有良好的光学、电学和化学性质,锐钛矿相TiO2具有更突出的光催化特性,是一种有广泛用途的宽禁带氧化物半导体。利用基于密度泛函理论的第一原理全电势线性缀加平面波方法计算锐钛矿相TiO2介电函数的实部、虚部和光学吸收系数,其中能隙值利用剪刀算符修正为3.2eV。计算结果与实验符合得很好,同时说明广义梯度近似与局域密度近似相比对锐钛矿相TiO2光学性质的计算没有明显的改善。

TiO2 is a wide-bandgap semiconductor with wide applications range, the anatase phase TiO2 has the better photocatalysis properties. In this paper, the optical properties of TiO2 with the anatase structure were in- vestigated using the full-potential linearized augmented plane-wave method （FPLAPW） in the framework of the density functional theory （DFT）. We amended band gaps by using a scissor operator, so that the minimum band gap shift becomes 3.2 eV in agreement with the experiment. Optical property calculation showed that a strong optical anisotropy near the absorption edge is observed. The calculated dielectric constants at ω→0 are ε1xy（O） （LDA） =5.52, ε1x（0）（LDA） =5.43 and ε1xy（0） （GGA） =5.42,ε1z（0） （GGA） =5.26. The dielectric functions have two main peaks. One is located between 4 and 6 eV, and the other is found at 8 -9 eV. As one can imagine, the two peaks are due to transition from states in the upper part of the valence bands （states） to states in the two lower Ti-3d conduction bands （π＊-dxy, and σ＇＊ states）. In a higher energy region （ 〉 7 eV） , the imaginary part of the calculated dielectric function peak positions are located at higher energies compared with experiment. Similar results were reported in calculations for the ruffle structure. The disagreement of the peak positions of the dielectric functions in a higher energy region suggests that a more sophisticated method going beyond the scissors operator to describe the quasiparticle spectrum of TiO2 is required. If we define the optical band edge as the photon energy where the value of α = 10^-4 cm ^-1, then the band edge Exy （LDA） = 3.52 eV, E. （LDA） = 3.93 eV and Exy （GGA） = 3.57 eV, Ex （GGA） = 3.96 eV, the results are in agreement with experiment, and the generalized gradient approximation （ GGA ） gives no improvement in comparison with the local density approximation （LDA） by investigating the optical properties.