论文标题
一项关于锂锰氧化锂的杂种密度功能理论基准研究
A Hybrid Density Functional Theory Benchmark Study on Lithium Manganese Oxides
论文作者
论文摘要
锂锰氧化物尖晶石李$ _x $ _2 $ _2 $ o $ _4 $，带有$ 0 \ leq x \ leq 2 $，是锂离子电池中阴极材料的重要例子。但是，对李$ _x $ _x $ _2 $ _2 $ o $ _4 $的准确描述，诸如密度功能理论之类的第一原理方法由于其复杂的电子结构而远非微不足道，并且具有各种能量封闭的电子和磁状态。已经发现，局部密度近似以及广义梯度近似（GGA）无法正确描述li $ _x $ mn $ _2 $ o $ $ _4 $。在这里，我们报告了使用混合功能PBE0和HSE06的不同Li $ _X $ _ $ _ $ o $ _z $系统的广泛基准，以及最近引入的本地混合功能PBE0R。我们发现所有这些功能都能与实验数据相吻合，从而产生能量，结构，电子和磁性。 PBE0R功能仅依赖于现场Hartree-fock交换的PBE0R功能的显着好处是，计算工作量大大减少，可与GGA功能相媲美。此外，PBE0R中的Hartree-fock混合因子比PBE0小，这改善了（锂）锰氧化物的结果。对Li $ _x $ MN $ _2 $ o $ _4 $的调查表明，两个Mn氧化状态 +III和 +IV，共处。 Mn $^\ text {iii} $ ions处于高旋转状态，相应的mno $ _6 $ contahedra被jahn-teller扭曲。 Mn $^\ text {iii} $和mn $^\ text {iv} $之间的比率，因此电子结构随li内容而变化，而在$ x = 0 $到$ 1 $的范围内没有重大结构变化。这项工作表明，PBE0R功能提供了对所研究的Li $ _X $ _X $ _ MN $ _Y $ o $ $ _z $ Systems的同样准确有效的描述。
The lithium manganese oxide spinel Li$_x$Mn$_2$O$_4$, with $0\leq x\leq 2$, is an important example for cathode materials in lithium ion batteries. However, an accurate description of Li$_x$Mn$_2$O$_4$ by first-principles methods like density functional theory is far from trivial due to its complex electronic structure, with a variety of energetically close electronic and magnetic states. It was found that the local density approximation as well as the generalized gradient approximation (GGA) are unable to describe Li$_x$Mn$_2$O$_4$ correctly. Here, we report an extensive benchmark for different Li$_x$Mn$_y$O$_z$ systems using the hybrid functionals PBE0 and HSE06, as well as the recently introduced local hybrid functional PBE0r. We find that all of these functionals yield energetic, structural, electronic, and magnetic properties in good agreement with experimental data. The notable benefit of the PBE0r functional, which relies on on-site Hartree-Fock exchange only, is a much reduced computational effort that is comparable to GGA functionals. Furthermore, the Hartree-Fock mixing factors in PBE0r are smaller than in PBE0, which improves the results for (lithium) manganese oxides. The investigation of Li$_x$Mn$_2$O$_4$ shows that two Mn oxidation states, +III and +IV, coexist. The Mn$^\text{III}$ ions are in the high-spin state and the corresponding MnO$_6$ octahedra are Jahn-Teller distorted. The ratio between Mn$^\text{III}$ and Mn$^\text{IV}$ and thus the electronic structure changes with the Li content while no major structural changes occur in the range from $x=0$ to $1$. This work demonstrates that the PBE0r functional provides an equally accurate and efficient description of the investigated Li$_x$Mn$_y$O$_z$ systems.
