(TiO_2)_(12)量子环及过渡金属化合物掺杂对其电子性质影响的密度泛函理论研究

Density functional theory studies of(TiO_2)_(12) quantum ring and its electronic properties when doped with transition metal compounds

本文采用第一性原理中基于密度泛函理论(DFT)的广义梯度近似(GGA)方法,设计了一种新的(TiO2)12量子环结构,研究了它的几何结构、平均结合能及电子云分布等属性.在此新型结构的基础上,分别采用过渡金属化合物MoS2,Mo Se2,Mo Te2,WS2,WSe2和WTe2进行掺杂,并分析了掺杂后体系的几何结构及电子属性(如平均结合能、能级结构、HOMO-LUMO轨道电子云密度分布和电子态密度等).计算结果表明:(TiO2)12量子环直径为1.059 nm,呈中心对称分布,且所有原子组成一个二维平面结构,使其几何结构比较稳定,另外该量子环HOMO-LUMO轨道电子云分布均匀,且能隙为3.17eV,与半导体材料TiO2晶体的能隙的实验值(3.2 eV)非常接近.掺杂后量子环的能隙均大幅减小,其中WTe2的掺杂结果能隙最小,仅为0.61eV,Mo Te2的掺杂结果能隙最大,为1.16 eV,也比掺杂前减小约2.0 eV.其他掺杂结果的能隙都在1eV左右,变化不大.这个能隙的TiO2可以利用大部分的太阳光能,使TiO2具有更为广泛的应用.

In this paper, we have designed a new（TiO2）12 quantum ring structure and studied its geometry, average binding energy, and the electron density distributions using the generalized gradient approximation（GGA）, which is based on the density functional theory（DFT） with the first-principles calculations. This new quantum ring structure is doped with transition metal compounds Mo S2, Mo Se2, Mo Te2, WS2, WSe2 and WTe2respectively, to modify its properties.Thus we can calculate and analyze their geometrics and electronic properties（such as average binding energies, energy levels, electronic density of states and the HOMO-LUMO electron density distributionsatc）. We find that the（TiO2）12quantum ring with a diameter of 1.059 nm seems to be of a two-dimensional structure with a center symmety which ensurs it a stable structure. In addition, the HOMO-LUMO orbital electron density in the quantum ring distributes evenly, and its energy gap is 3.17 eV which is very close to the experimental value of TiO2 semiconductor materials（3.2eV）. The energy gaps decrease substantially after introducing the transition metal compounds into the quantum ring.Among these results, the ring doped with WTe2 has the smallest energy gap（0.61 eV）, and that with Mo Te2 has the biggest energy gap（1.16 eV）, but it is still smaller by about 2 eV than that of the（TiO2）12 quantum ring. Furthermore,other doping results have energy gap variation around 1 eV. The TiO2 clusters with this energy gap could make use most of the solar energy and so expand applications of TiO2.