Systematic density functional theory-based first principles studies on As K-edge electron energy loss near edge structures are presented for rare earth (RE)-doped iron-based superconducting materials ${\text{Ca}}_{1-\text{x}}{\text{RE}}_{\text{x}}{\text{FeAs}}_2$ (known as 112 compounds). The As K-edge electron energy losses near edge differ for two different types of As atoms (belonging to Fe–As plane and ${\text{As}}_2$ chains between the planes). The As K-edge spectra (of both As atoms in chain and plane) are very sensitive to the nature of RE doping (RE = La, Ce, Pr, Nd, Sm, Gd). For example, the As K-edge shifts to higher energies successively with decreasing RE size (La $\to$ Gd), indicating larger binding energies and hence stability of the corresponding compound. In contrast, the white-line peak successively shifts to lower energies for La $\to$ Gd doping, resulting in complete suppression of another low energy absorption peak for Gd. These are in essence an artifact of heavy electron doping caused by RE atoms. Interrelationship between the electron doping and corresponding shift in the white-line feature for various RE-doped samples is established through Bader charge analysis. Each absorption spectra consists of several peaked features of particular significance; they are thoroughly analyzed in terms of the unoccupied partial density of states. To emphasize the influence of the “core-hole” effect, absorption spectra in the presence and absence of core-holes are presented separately. Relevance of our results with respect to experimental scenarios are also discussed.

提出了基于系统密度泛函理论的稀土（RE）掺杂铁基超导材料边缘结构附近As K-边缘电子能量损失的第一性原理研究${\text{钙}}_{\mathrm{1个}-\text{X}}{\text{回覆}}_{\text{X}}{\text{砷化铁}}_{\mathrm{2个}}$（称为112种化合物）。的As ķ _edge时电子能量近边缘损失差异，两种不同类型的As原子的（属于铁作为平面和${\text{作为}}_{\mathrm{2个}}$飞机之间的链条）。（链中和平面中的两个As原子的）As K边缘光谱对RE掺杂的性质（RE = La，Ce，Pr，Nd，Sm，Gd）非常敏感。例如，随着RE尺寸的减小，As K边沿相继转移到更高的能量（La$\to$Gd），表示较大的结合能，因此表示相应化合物的稳定性。相反，对于La，白线峰值依次移至较低的能量$\to$Gd掺杂，导致完全抑制了Gd的另一个低能量吸收峰。这些本质上是由RE原子引起的重电子掺杂的假象。通过Bader电荷分析，建立了各种RE掺杂样品的电子掺杂与白线特征的相应偏移之间的相互关系。每个吸收光谱都包含几个具有特别重要意义的峰形特征。根据未占用的部分状态密度对它们进行了彻底的分析。为了强调“核心孔”效应的影响，分别介绍存在和不存在核心孔的吸收光谱。还讨论了我们的结果与实验场景的相关性。