插层化合物Li_xTiS_2中Li离子-空位二维有序结构稳定性的第一性原理研究

First principles computational study on the stability of Li ion-vacancy two-dimensional ordered structures in intercalation compounds Li_xTiS_2

根据局域密度近似下的密度泛函理论,用第一性原理方法对TiS2,LiTiS2和LixTiS2(x=1/4,1/3,1/2,2/3,3/4)有序系统进行了几何优化和总能量计算.将计算结果与已有的实验和理论结果进行了对比,得到的归一化结构参量增量Δa0和Δc0随离子浓度单调地增加,与实验结果符合较好.LixTiS2(x=1/4,1/3,1/2,2/3,3/4)有序结构的形成能均小于零,表明这些结构的稳定性.具有3a0×a0有序结构的Li1/2TiS2系统的形成能最低、结构最稳定.研究结果表明,对上述系统使用局域密度近似下的密度泛函理论是合理的.

Geometry optimization and total energy computation were carried out for TiS2, LiTiS2 and intercalation compound LixTiS2 （ x = 1/4, 1/3, 1/2, 2/3, 3/4）ordered systems using first principles method based on local density approximation to density- functional theory. The computation results for these systems have been compared with other experimental and theoretical results available in the literature. The normalized increments of lattice parameters △a0 and △c0 increase monotonicly with the increasing concentration of Li ion. The curves show good agreement with lattice parameters obtained from experiment. The formation energies of ordered systems Lix TiS2 （ x = 1/4, 1/3, 1/2, 2/3, 3/4） are all negative, indicating their stability at low temperature. The formation energy of Li1/2 TiS2 system with √3α0×α0 ordered structure is the lowest, implying the most stable structure. The results have shows that the local density approximation to density-functional theory can reasonably be applied to TiS2 , LiTiS2 and intercalation compound Lix TiS2 （ x = 1/4, 1/3, 1/2, 2/3, 3/4） ordered systems.