Multiscale QM/MM molecular dynamics simulations of the trimeric major light-harvesting complex II. Issue 12 (23rd March 2021)

• Record Type: Journal Article
• Authors: Maity, Sayan; Daskalakis, Vangelis; Elstner, Marcus; Kleinekathöfer, Ulrich
• Is Part Of: Physical chemistry chemical physics. Volume 23:Issue 12(2021)
• Page Start: 7407
• Page End: 7417
• Publication Date: 2021-03-23
• Subjects: Chemistry, Physical and theoretical -- Periodicals; 541.3
• DOI: 10.1039/d1cp01011e
• Languages: English
• ISSNs: 1463-9076

Abstract

Abstract : The site energies and spectral densities of the major light-harvesting complex LHCII have been determined using QM/MM molecular dynamics simulations. In particular, the spectral densities show a remarkable agreement with experimental findings. Abstract : Photosynthetic processes are driven by sunlight. Too little of it and the photosynthetic machinery cannot produce the reductive power to drive the anabolic pathways. Too much sunlight and the machinery can get damaged. In higher plants, the major Light-Harvesting Complex (LHCII) efficiently absorbs the light energy, but can also dissipate it when in excess (quenching). In order to study the dynamics related to the quenching process but also the exciton dynamics in general, one needs to accurately determine the so-called spectral density which describes the coupling between the relevant pigment modes and the environmental degrees of freedom. To this end, Born–Oppenheimer molecular dynamics simulations in a quantum mechanics/molecular mechanics (QM/MM) fashion utilizing the density functional based tight binding (DFTB) method have been performed for the ground state dynamics. Subsequently, the time-dependent extension of the long-range-corrected DFTB scheme has been employed for the excited state calculations of the individual chlorophyll-a molecules in the LHCII complex. The analysis of this data resulted in spectral densities showing an astonishing agreement with the experimental counterpart in this rather large system. This consistency with an experimental observable also supports the accuracy, robustness, and reliability of the present multi-scale scheme. To the best of our knowledge, this is the first theoretical attempt on this large complex system is ever made to accurately simulate the spectral density. In addition, the resulting spectral densities and site energies were used to determine the exciton transfer rate within a special pigment pair consisting of a chlorophyll-a and a carotenoid molecule which is assumed to play a role in the balance between the light harvesting and quenching modes.