电子掺杂有机物：电荷不成比例绝缘体和Hubbard-Fröhlich金属
Electron-doped organics: Charge-disproportionate insulators and Hubbard-Fröhlich metals
摘要：
金属电子掺杂的多环芳烃（PAHs）分子晶体的几个例子最近已被实验提出。其中一些具有超导成分，但大多数其他细节仍然未知，首先是结构和金属性的性质。我们进行了从头算密度泛函计算的La-菲（La-PA），在这里意味着代表一个通用的情况下，三电子掺杂，调查的结构和性质的一个概念上简单的情况。令我们惊讶的是，我们首先发现，最低的能量状态是不是金属，但带绝缘，与两个不等价的PA分子离子和低的P1对称性，质疑常见的假设，三个电子将自动金属化的PAH晶体。我们最好的金属结构是亚稳态的，能量略高，并保留了等效的PA离子和更高的P21对称性-通常对金属多环芳烃的要求相同。我们发现，一个“二聚化”的周期性畸变打开非常有效的间隙，在费米能级附近的所有P21结构的对称性相关的简并性的地方，预示着一个可能的作用，特殊的分子间声子在金属多环芳烃的超导性。描述这种情况的Hubbard-Frohlich模型制定了未来的研究。
英文摘要：
Several examples of metallic electron doped polycyclic aromatic hydrocarbons (PAHs) molecular crystals have recently been experimentally proposed. Some of them have superconducting components, but most other details are still unknown beginning with structure and the nature of metallicity. We carried out ab-initio density functional calculations for La-Phenanthrene (La-PA), here meant to represent a generic case of three-electron doping, to investigate structure and properties of a conceptually simple case. To our surprise we found first of all that the lowest energy state is not metallic but band insulating, with a disproportionation of two inequivalent PA molecular ions and a low P1 symmetry, questioning the common assumption that three electrons will automatically metallize a PAH crystal. Our best metallic structure is metastable and slightly higher in energy, and retains equivalent PA ions and a higher P21 symmetry -- the same generally claimed for metallic PAHs. We show that a "dimerizing" periodic distortion opens very effectively a gap in place of a symmetry related degeneracy of all P21 structures near the Fermi level, foreshadowing a possible role of that special intermolecular phonon in superconductivity of metallic PAHs. A Hubbard-Frohlich model describing that situation is formulated for future studies.
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