Significant Reduction of On-Site Coulomb Energy U due to Short-Range Correlation in an Organic Mott Insulator

• Published in: Chemphyschem 2006-08, Vol.7 (8), p.1820-1824
• Main Authors: Ohno, Kaoru, Noguchi, Yoshifumi, Yokoi, Toshihiro, Ishii, Soh, Takeda, Jun, Furuya, Miou
• Format: Article
• Language: English
• Subjects: Ab initio calculations; Atomic and molecular physics; Calculations and mathematical techniques in atomic and molecular physics (excluding electron correlation calculations); Coulomb hole; dimerization; Electronic structure of atoms, molecules and their ions: theory; Exact sciences and technology; first-principles calculations; phase transitions; Physics; radicals
• ISSN: 1439-4235; 1439-7641
• DOI: 10.1002/cphc.200600144

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. Influential short range: In a Mott insulator of the organic radical 1,3,5‐trithia‐2,4,6‐triazapentalenyl (TTTA), the two‐electron probability distribution (see figure) obtained by first‐principles (multiple scattering) T matrix calculations, indicates clearly the formation of a “Coulomb hole”. This short‐range electron correlation reduces significantly the on‐site Coulomb energy.