Cu掺杂KCl折叠和展开能带结构及光学性质的DFT计算
Cu-Doped KCl folded and unfolded band structure and optical properties studied by DFT calculations
摘要：
计算了掺铜KCl晶体的光学性质以及折叠和展开的能带结构。计算使用平面波赝势的方法在第一性原理密度泛函理论框架内的ABINIT电子结构包中实现。铜取代到原始氯化钾晶体需要计算的超原胞（SC）方法从理论的角度来看。这一过程缩小了布里渊区，导致难以解释的折叠能带结构。为了解决这一问题，深入了解铜离子（Cu+）对电子性质的影响，我们展开了SC KCl：Cu的能带结构，并与原始KCl的原胞（PC）的能带结构进行了直接比较.为了理解Cu取代对光吸收的影响，我们通过一个sum-over-states形式主义计算了KCl：Cu的介电函数的虚部，并通过部分地对选定的价带和导带进行迭代累积和（ICS）来将其分解为不同的能带贡献。因此，我们确定了那些带间跃迁，引起的吸收峰，由于铜离子。这些跃迁包括由Cu-3d和Cu-4s电子态形成的价带和导带。为了研究掺杂位置的影响，我们考虑了不同的掺杂位置，其中Cu掺杂剂占据了所有的替代位点，取代了宿主K阳离子。结果表明，掺杂位置的影响导致了几何结构中的两种八面体形状。扭曲扭曲的八面体正方形双锥几何形状诱导的晶体场分裂能量相比，完美的八面体正方形双锥几何形状的差异。
英文摘要：
We computed the optical properties and the folded and unfolded band structure of Cu-doped KCl crystals. The calculations use the plane-wave pseudo-potential approach implemented in the ABINIT electronic structure package within the first-principles density-functional theory framework. Cu substitution into pristine KCl crystals requires calculation by the supercell (SC) method from a theoretical perspective. This procedure shrinks the Brillouin zone, resulting in a folded band structure that is difficult to interpret. To solve this problem and gain insight into the effect of cuprous ion (Cu+) on electronic properties; We unfolded the band structure of SC KCl:Cu to directly compare with the band structure of the primitive cell (PC) of pristine KCl. To understand the effect of Cu substitution on optical absorption, we calculated the imaginary part of the dielectric function of KCl:Cu through a sum-over-states formalism and broke it down into different band contributions by partially making an iterated cumulative sum (ICS) of selected valence and conduction bands. As a result, we identified those interband transitions that give rise to the absorption peaks due to the Cu ion. These transitions include valence and conduction bands formed by the Cu-3d and Cu-4s electronic states. To investigate the effects of doping position, we consider different doping positions, where the Cu dopant occupies all the substitutional sites replacing host K cations. Our results indicate that the doping position's effects give rise to two octahedral shapes in the geometric structure. The distorted-twisted octahedral square bipyramidal geometric-shape induces a difference in the crystal field splitting energy compared to that of the perfect octahedral square bipyramidal geometric-shape.
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