title: Significant reduction of on-site Coulomb energy U due to short-range correlation in an organic Mott insulator.
abstract: By carrying out a first-principles T-matrix calculation on multiple scatterings between electrons, we show that the intramolecular electron-electron interaction energy U, of a Mott insulator of the organic radical 1,3,5-trithia-2,4,6-triazapentalenyl (TTTA) is significantly reduced from the naive expectation value of the Coulomb interaction (7.3 eV and 5.3 eV, respectively, for the bare and screened Coulomb interactions) to 2.9 eV due to the short-range correlation. This result together with the intermolecular interaction energy D=1.3 eV explains the experimental optical gap (1.5 eV). The associated two-particle wavefunction clearly shows the Coulomb hole indicating that two electrons with antiparallel spins cannot approach because of the Coulomb repulsion. We also discuss the energetics and magnetics of this system.
authors.affiliation: Department of Physics, Yokohama National University, 79-5 Tokiwadai, Hodogaya, Yokohama 240-8501, Japan. ohno@ynu.ac.jp
authors.forename: Kaoru
authors.initials: K
authors.lastname: Ohno
authors.forename: Yoshifumi
authors.initials: Y
authors.lastname: Noguchi
authors.forename: Toshihiro
authors.initials: T
authors.lastname: Yokoi
authors.forename: Soh
authors.initials: S
authors.lastname: Ishii
authors.forename: Jun
authors.initials: J
authors.lastname: Takeda
authors.forename: Miou
authors.initials: M
authors.lastname: Furuya