First-Principles Calculation of the Superconducting TransitionTemperature with determining the Coulomb Pseudopotential

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By considering the correspondence between the Green’s-function approach and the density-functional theory for superconductors (SCDFT), we have constructed a new functional form for the pairing potential appearing in the gap equation in the SCDFT, which enables us to calculate the superconducting transition temperature T_ from first principles with the determination of the Coulomb pseudopotential. We have applied this framework to the graphite intercalation compounds (GICs) and clarified the microscopic mechanism of superconductivity in GICs. We have also made a theoretical search for a path to synthesize GICs with higher T_, as well as to obtain high-temperature superconductors for which we conclude that strong phonon-mediated interactions with almost cancelling strong electron-electron repulsions are needed.