LaMnO_3的结构畸变和模型哈密顿参数：从LSDA到紧束缚描述
Structural distortions and model Hamiltonian parameters: from LSDA to a tight-binding description of LaMnO_3
摘要：
锰氧化物的物理学通常在Mn e_g电子的有效双带紧束缚（TB）模型内描述，除了动能之外，该模型还包括与t_{2g}核心自旋的局部“Hund规则”耦合和与氧八面体的Jahn-Teller（JT）畸变的局部耦合。我们测试这个模型的有效性，通过比较TB模型计算的能量色散与本地自旋密度近似（LSDA）内计算的全Kohn-Sham带结构密度泛函理论。我们分析了氧八面体的磁有序、JT畸变和“GdFeO_3型”倾斜旋转的影响。我们表明，跳跃幅度是独立的磁序和JT失真，这两种效果可以描述一组一致的模型参数，如果考虑到最近和次最近的邻居之间的跳跃。我们从密度泛函理论计算中确定了一套完整的模型参数，并且我们表明，JT扭曲和Hund规则耦合都需要在LSDA内获得绝缘基态。此外，我们的计算表明，“GdFeO_3型”的氧八面体的旋转导致跳跃幅度的显着减少，但没有显着偏离简单的TB模型。
英文摘要：
The physics of manganites is often described within an effective two-band tight-binding (TB) model for the Mn e_g electrons, which apart from the kinetic energy includes also a local "Hund's rule" coupling to the t_{2g} core spin and a local coupling to the Jahn-Teller (JT) distortion of the oxygen octahedra. We test the validity of this model by comparing the energy dispersion calculated for the TB model with the full Kohn-Sham band-structure calculated within the local spin-density approximation (LSDA) to density functional theory. We analyze the effect of magnetic order, JT distortions, and "GdFeO_3-type" tilt-rotations of the oxygen octahedra. We show that the hopping amplitudes are independent of magnetic order and JT distortions, and that both effects can be described with a consistent set of model parameters if hopping between both nearest and next-nearest neighbors is taken into account. We determine a full set of model parameters from the density functional theory calculations, and we show that both JT distortions and Hund's rule coupling are required to obtain an insulating ground state within LSDA. Furthermore, our calculations show that the "GdFeO_3-type" rotations of the oxygen octahedra lead to a substantial reduction of the hopping amplitudes but to no significant deviation from the simple TB model.
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