锐钛矿型TiO_2(101)面原子几何及弛豫结构的第一性原理计算

First-principle calculations on the geometry and relaxation structure of anatase TiO_2(101) surface

采用平面波超软赝势方法计算了锐钛矿型TiO2(101)面的表面能和表面原子弛豫结构.首先对TiO2(101)面的6种不同的表面原子终止结构的体系总能量进行了计算,结果表明终止原子为两配位的O原子、次层为五配位的Ti原子的表面结构最为稳定.针对该表面研究了表面能和原子弛豫与模型中原子层数和真空厚度的关系,当原子层数为12层,真空厚度为0.4nm时,表面能收敛度小于0.01Jm2.研究发现:表面上两配位的O原子向里移动约0.0012nm,五配位的Ti原子向里移动约0.0155nm,弛豫后的Ti—O键长发生了较大变化,核外电荷发生了转移,结构趋于稳定.

First-principle calculations based on the plane-wave pseudopotential method have been used to study the surface energy and structure of anatase TiO2 （ 101 ） surface. There are six different structures of the anatase TiO2 （ 101 ） crystal surface because different atoms are terminated on the surface layers. The calculation result shows that anatase TiO2 （101） crystal surface structure which the outermost and second layer respectively terminated by twofold coordinated oxygen atoms and fivefold coordinated titanium atoms is much more stable than the other five structures. By investigating the effect of variable vacuum layer thickness and slab thickness on the surface energy and surface atomic displacements, we find that slab thicknesses of at least 12 atom layers and vacuum layer thickness of more 0.4 nm are sufficient to converge the surface energy to within 0.01 J/m^2 . At last, we obtained the result that the twofold coordinated oxygen atoms have an inward relaxation of 0.0012 nm, and fivefold coordinated titanium atoms have an outward relaxation of 0.0155 nm, while the length of Ti-O bonds and quantity of electric charge of titanium and oxygen atoms are changed, making the structure more stable.