三钾掺杂碳氢化合物超导体的几何和电子结构：密度泛函计算
Geometrical and electronic structures of tripotassium-doped hydrocarbon superconductors: Density functional calculations
摘要：
由于多环芳烃（PAHs）在钾离子掺杂下表现出超导电性，本文系统地研究了它们的晶体结构和电子性质，如固体菲、1，2; 8，9-二苯并五苯、7-并苯等。对于三钾掺杂的菲和芘，我们证明了K原子的位置来拟合实验晶格参数，并分析了最稳定构型与拟合的实验构型之间的区别。基于第一性原理计算，我们首次预测了1，2; 8，9-二苯并五苯和7-并苯的晶体构型.对于这四种多环芳烃，掺杂后的电子结构进行了详细的研究。结果表明，费米能级附近的电子特性对结构具有很高的敏感性。1，2; 8，9-二苯并五苯由于苯环排列的改变，其能带结构与其它三种多环芳烃明显不同。在这些金属多环芳烃中，有两个带穿过费米能级，这导致了费米面复杂的多带特征。有趣的是，我们发现钾的电子态对费米面有贡献，特别是对K-3 $d$电子，这改进了理解这种超导性的方法。结果表明，由于K原子与PAH分子的杂化以及PAH分子的重排和畸变，刚性带图像是无效的。
英文摘要：
A systemically theoretical study has been presented to explored the crystal structures and electronic characteristics of polycyclic aromatic hydrocarbons (PAHs), such as solid phenanthrene, picene, 1,2;8,9-dibenzopentacene, and 7-phenacenes, since these PAHs exhibited the superconductivity when potassium doping into. For tripotassium-doped phenanthrene and picene, we demonstrate the K atomic positions to fit the experimental lattice parameters, and analyze the distinction between the stablest configuration and the fitted experimental one. Based on the first-principles calculations, for the first time, we predict the possible crystal configurations of pristine and tripotassium-doped 1,2;8,9-dibenzopentacene and 7-phenacenes, respectively. For these four PAHs, the electronic structures after doping are investigated in details. The results show that the electronic characters near the Fermi level are high sensitive to structure. Because of the change of the benzene rings arrangement, the 1,2;8,9-dibenzopentacene exhibits visibly different band structures from other three PAHs. In these metallic PAHs, two bands cross the Fermi level which results in the complicated multiband feature of Fermi surfaces. Fascinatingly, we find that the electronic states of potassium contribute to the Fermi surfaces especially for K-3$d$ electrons, which improves a way to understand this superconductivity. As a result, we suggest that the rigid-band picture is invalidated due to the hybridization between K atoms and PAH molecules as well as the rearrangement and distortion of PAH molecules.
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