Electron-doped organics: Charge-disproportionate insulators and Hubbard-Fröhlich metals

Abstract

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.

9 pages and 7 figures

References in corpus (8)

• Quantum ESPRESSO: a modular and open-source software project for quantum simulations of materials
• A Higher-Accuracy van der Waals Density Functional
• Absence of a Spin Liquid Phase in the Hubbard Model on the Honeycomb Lattice
• Modeling the Unconventional Superconducting Properties of Expanded A${}_3$C${}_{60}$ Fullerides
• Electronic Correlation effects in superconducting picene from ab-initio calculations
• Vibrational spectrum and electron-phonon coupling of doped solid picene from first principles
• Absence of photoemission from the Fermi level in potassium intercalated picene and coronene films: structure, polaron or correlation physics?
• Local and non-local electron-phonon couplings in K3Picene and the effect of metallic screening

Cited by in corpus (5)

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• Stable structural phase of potassium-doped p-terphenyl and its semiconducting state
• Van der Waals density functional study of the structural and electronic properties of La-doped phenanthrene
• Robust $s\pm$ Superconductivity in a Two-Band Hubbard-Fr{ö}hlich Model of Alkali Doped Organics