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Excitation Spectra of Retinal by Multiconfiguration Pair-Density Functional Theory

Abstract

Retinal is the chromophore in proteins responsible for vision. The absorption maximum of retinal is sensitive to mutations of the protein. However, it is not easy to predict the absorption spectrum of retinal accurately, and questions remain even after intensive investigation. Retinal poses a challenge for Kohn-Sham density functional theory (KS-DFT) because of the charge transfer character in its excitations, and it poses a challenge for wave function theory because the large size of the molecule makes multiconfigurational perturbation theory methods expensive. In this study, we demonstrate that multiconfiguration pair-density functional theory (MC-PDFT) provides an efficient way to predict the vertical excitation energies of 11-Z retinal, and it reproduces the experimentally determined absorption band widths and peak positions better than complete active space second-order perturbation theory (CASPT2). The consistency between complete active space self-consistent field (CASSCF) and KS-DFT dipole moments is demonstrated to be a useful criterion in selecting the active space. We also found that the conformations of retinal play a significant role in the absorption spectrum. By considering a thermal distribution of conformations, we predict an absorption spectrum of retinal that is consistent with experimental gas-phase spectrum. The location of the absorption peak and the spectral broadening based on MC-PDFT calculations agree better with experiments than CASPT2.

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Publication details

The article was received on 27 Oct 2017, accepted on 08 Feb 2018 and first published on 08 Feb 2018


Article type: Paper
DOI: 10.1039/C7CP07275A
Citation: Phys. Chem. Chem. Phys., 2018, Accepted Manuscript
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    Excitation Spectra of Retinal by Multiconfiguration Pair-Density Functional Theory

    S. S. Dong, L. Gagliardi and D. G. Truhlar, Phys. Chem. Chem. Phys., 2018, Accepted Manuscript , DOI: 10.1039/C7CP07275A

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