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Analysis of spin-density wave conductivity spectra of iron pnictides in the framework of density functional theory

机译：密度泛函理论框架下铁离子的自旋密度波电导谱分析

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The optical conductivity of LaFeAsO, BaFe_2As_2, SrFe_2As_2, and EuFe_2As_2 in the spin-density wave (SDW) state is investigated within density functional theory (DFT) in the framework of spin-polarized generalized gradient approximation (GGA) and GGA+U. We find a strong dependence of the optical features on the Fe magnetic moments. In order to recover the small Fe magnetic moments observed experimentally, GGA+U-(eff) with a suitable choice of negative on-site interaction U_(eff)= U-J was considered. Such an approach may be justified in terms of an overscreening which induces a relatively small U compared to the Hund's rule coupling 7, as well as a strong Holstein-type electron-phonon interaction. Moreover, reminiscent of the fact that GGA+ U_(eff) with a positive U_(eff) is a simple approximation for reproducing a gap with correct amplitude in correlated insulators, a negative U_(eff) can also be understood as a way to suppress magnetism and mimic the effects of quantum fluctuations ignored in DFT calculations. With these considerations, the resulting optical spectra reproduce the SDW gap and a number of experimentally observed features related to the antiferromag-netic order. We find electronic contributions to excitations that so far have been attributed to purely phononic modes. Also, an orbital-resolved analysis of the optical conductivity reveals significant contributions from all Fe 3d orbitals. Finally, we observe that there is an important renormalization of kinetic energy in these SDW metals, implying that the effects of correlations cannot be neglected.
机译：在自旋极化广义梯度近似（GGA）和GGA + U的框架下，在密度泛函理论（DFT）中研究了自旋密度波（SDW）状态下LaFeAsO，BaFe_2As_2，SrFe_2As_2和EuFe_2As_2的光导率。我们发现光学特征对铁磁矩的强烈依赖性。为了恢复实验中观察到的小Fe磁矩，考虑了采用负现场相互作用U_（eff）= U-J的适当选择的GGA + U-（eff）。这样的方法可以通过过筛来证明是合理的，该过筛会导致与洪德法则耦合7相比相对较小的U以及强大的荷斯坦型电子-声子相互作用。此外，令人联想到具有正U_（eff）的GGA + U_（eff）是在相关绝缘子中再现具有正确振幅的间隙的简单近似值，负U_（eff）也可以理解为抑制磁性的一种方式并模拟DFT计算中忽略的量子涨落的影响。考虑到这些因素，所得的光谱会再现SDW间隙以及许多与反铁磁阶有关的实验观察到的特征。我们发现到目前为止，对激发的电子贡献一直归因于纯声子模式。而且，对轨道的光学传导率分析表明，所有Fe 3d轨道都有重要贡献。最后，我们观察到这些SDW金属中的动能有重要的重新归一化，这意味着相关性的影响不可忽略。

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