Superconductivity in an Effective Model Derived from Wannier Orbitals for an Organic Conductor (TMTSF)2ClO4

We perform first-principles band calculations and derive an effective tight-binding model for a quasi-one-dimensional organic conductor (TMTSF)2ClO4. The first-principles band structures show four bands near the Fermi level. Since four TMTSF molecules are present in the unit cell, we regard a TMTSF molecule as a site and derive an effective tight-binding model exploiting the maximally localized Wannier orbitals. The outer Fermi surface almost contacts the inner one as in the previous studies. We introduce the on-site repulsive interaction and deal with the electron correlation applying the two-particle self-consistent (TPSC) method. The diagonalized spin susceptibility takes large values at the nesting vector between the outer and inner Fermi surfaces. Assuming a pairing mechanism mediated by the spin fluctuations, it is found that the sign of the superconducting gap in the spin-singlet channel changes between the outer and inner Fermi surfaces.