期刊
JOURNAL OF CHEMICAL THEORY AND COMPUTATION
卷 13, 期 9, 页码 4357-4367出版社
AMER CHEMICAL SOC
DOI: 10.1021/acs.jctc.7b00505
关键词
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资金
- Labex MiChem part of French state funds [ANR-11-IDEX-0004-02]
- computational centre of the Laboratoire de Chimie Theorique
- University of L'Aquila
- European Union [H2020-EINFRA-2015-1, 676598]
- European Research Council Project MultiscaleChemBio within the VII Framework Program of the European Union [240624]
The structures of three negatively charged forms (anionic keto-1 and enol-1 and dianionic enol-2) of oxyluciferin (OxyLuc), which are the most probable emitters responsible for the firefly bioluminescence, have been fully relaxed at the variational Monte Carlo (VMC) level. Absorption energies of the S-1 -> S-0 vertical transition have been computed using different levels of theory, such as TDDFT, CC2, and many-body Green's function theory (MBGFT). The use of MBGFT, by means of the Bethe-Salpeter (BS) formalism, on VMC structures provides results in excellent agreement with the value (2.26(8) eV) obtained by action spectroscopy experiments for the keto-1 2 form (2.32 eV). To unravel the role of the quality of the optimized ground-state geometry, BS excitation energies have also been computed on CASSCF. geometries, inducing a non-negligible blue shift (0.08 and 0.07 eV for keto-1 and enol-1 forms, respectively) with respect to the VMC ones. Structural effects have been analyzed in terms of over- or undercorrelation along the conjugated of OxyLuc by using different methods for the ground-state optimization. The relative stability of the S-1 state for the keto-1 and enol-1 forms depends on the method chosen for the excited-state calculation, thus representing a fundamental caveat for any theoretical study on these systems. Finally, Kohn-Sham HOMO and LUMO orbitals of enol-2 are (nearly) bound only when the dianion is embedded into a solvent (water and toluene in the present work); excited-state calculations are therefore meaningful only in the presence of a dielectric medium which localizes the electronic density. The combination of VMC for the ground-state geometry and BS formalism for the absorption spectra clearly outperforms standard TDDFT and quantum chemistry approaches.
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