第一性原理计算C掺杂金红石型TiO_2的磁性和光学性质

First-principles calculations for the magnetisms and optical properties of C-doped rutile TiO_2

本文运用第一性原理GGA+U方法计算了C元素单/双掺杂金红石型TiO_2的电子结构、磁性和光学性质.结果表明,C掺杂体系的晶格发生畸变和体积相应增大.单掺杂体系的磁矩为1.3μB,磁矩主要归因于杂质态引起的自旋电荷密度不平衡,杂质态主要由C-2p、O-2p和Ti-3d的态电子构成,且它们之间存在明显的杂化现象.双掺杂体系中C原子之间的反铁磁性耦合比铁磁性耦合更加稳定,但其磁矩为零.另外,随着掺杂浓度的增大,掺杂体系的带隙由2.58 eV增大到3.4 eV,且在可见光区域的光吸收效率明显增大.这表明带隙的减小可能不是光谱吸收增强的主要因素,而带隙中的杂质态极大地影响了光谱吸收效率.

The electronic structures, magnetisms and optical properties of C element single / double - doped rufile TiO2 are investigated by the first - principles calculations of generalized gradient approximation （GGA） ＋ U method. The computational results show that the C - doping system is distorted and the volume increases accordingly. The magnetic moment of the single - doping system is 1.3 μB. It is mainly due to the imbalance of spin - charge density which is caused by impurity states. The impurity states are mainly contributed by the C -2p states, O-2p states and Ti-3d states. And there is an obvious hybridization phenomenon between them. The antiferromagnetic coupling of among C atoms is more stable than ferromagnetic coupling in double - doped system. But the ferromagnetic system is no magnetic moment. In addition, with the increase of the doping concentration, the band gap of doping system increases from 2. 58 eV to 3.4 eV. And the absorption efficiency of light has a significant increase in the visible region. It indicates that the decrease of band gap is not major factor about spectral absorption enhancement. The impurity states in the band gap greatly affect the spectral absorption efficiency.