title: Ab Initio Geometry and Bright Excitation of Carotenoids: Quantum Monte Carlo and Many Body Green's Function Theory Calculations on Peridinin.
abstract: In this letter, we report the singlet ground state structure of the full carotenoid peridinin by means of variational Monte Carlo (VMC) calculations. The VMC relaxed geometry has an average bond length alternation of 0.1165(10) Å, larger than the values obtained by DFT (PBE, B3LYP, and CAM-B3LYP) and shorter than that calculated at the Hartree-Fock (HF) level. TDDFT and EOM-CCSD calculations on a reduced peridinin model confirm the HOMO-LUMO major contribution of the Bu(+)-like (S2) bright excited state. Many Body Green's Function Theory (MBGFT) calculations of the vertical excitation energy of the Bu(+)-like state for the VMC structure (VMC/MBGFT) provide an excitation energy of 2.62 eV, in agreement with experimental results in n-hexane (2.72 eV). The dependence of the excitation energy on the bond length alternation in the MBGFT and TDDFT calculations with different functionals is discussed.
authors.affiliation: Dipartimento di Scienze Fisiche e Chimiche, Università degli Studi dell'Aquila , via Vetoio, 67110 L'Aquila, Italy.
authors.forename: Emanuele
authors.initials: E
authors.lastname: Coccia
authors.affiliation: S3 Center, CNR Institute of Nanoscience , Via Campi 213/A, 41125 Modena, Italy.
authors.forename: Daniele
authors.initials: D
authors.lastname: Varsano
authors.affiliation: Dipartimento di Scienze Fisiche e Chimiche, Università degli Studi dell'Aquila , via Vetoio, 67110 L'Aquila, Italy.
authors.forename: Leonardo
authors.initials: L
authors.lastname: Guidoni