Atomistic non-adiabatic dynamics of the LH2 complex with a GPU-accelerated ab initio exciton model
| Autor: | Simon McIntosh-Smith, Michael B. O'Connor, Aaron Sisto, David R. Glowacki, Clem Stross, Graham T. Johnson, Frederick R. Manby, Marc W. van der Kamp, Todd J. Martínez, Edward G. Hohenstein |
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| Rok vydání: | 2017 |
| Předmět: |
Physics
Physics::Biological Physics education.field_of_study 010304 chemical physics Exciton Population Ab initio General Physics and Astronomy Surface hopping Time-dependent density functional theory 010402 general chemistry 01 natural sciences 0104 chemical sciences Molecular dynamics Delocalized electron Excited state 0103 physical sciences Physics::Chemical Physics Physical and Theoretical Chemistry Atomic physics education |
| Zdroj: | Sisto, A, Van der Kamp, M, Stross, C, O'Connor, M, McIntosh-Smith, S, Johnson, G T, Hohenstein, E G, Manby, F, Glowacki, D & Martinez, T 2017, ' Atomistic non-adiabatic dynamics of the LH2 complex with a GPU-accelerated ab initio exciton model ', Physical Chemistry Chemical Physics, vol. 19, no. 23, pp. 14924-14936 . https://doi.org/10.1039/c7cp00492c |
| ISSN: | 1463-9084 1463-9076 |
| Popis: | We recently outlined an efficient multi-tiered parallel ab initio excitonic framework that utilizes time dependent density functional theory (TDDFT) to calculate ground and excited state energies and gradients of large supramolecular complexes in atomistic detail – enabling us to undertake nonadiabatic simulations which explicitly account for the coupled anharmonic vibrational motion of all the constituent atoms in a supramolecular system. Here we apply that framework to the 27 coupled bacterio-cholorophyll-a chromophores which make up the LH2 complex, using it to compute an onthe-fly nonadiabatic surface-hopping (SH) trajectory of electronically excited LH2. Part one of this article is focussed on calibrating our ab initio exciton Hamiltonian using two key parameters: a shift δ, which corrects for the error in TDDFT vertical excitation energies; and an effective dielectric constant ε, which describes the average screening of the transition-dipole coupling betweenchromophores. Using snapshots obtained from equilibrium molecular dynamics simulations (MD) of LH2, we tune the values of both δ and ε through fitting to the thermally broadened experimental absorption spectrum, giving a linear absorption spectrum that agrees reasonably well with experiment. In the part two of this article, we construct a time-resolved picture of the coupledvibrational and excitation energy transfer (EET) dynamics in the sub-picosecond regime following photo-excitation. Assuming Franck-Condon excitation of a narrow eigenstate band centred at 800 nm, we use surface hopping to follow a single nonadiabatic dynamics trajectory within the full eigenstate manifold. Consistent with experimental data, this trajectory gives timescales forB800 → B850 population transfer (τ B800→B850 ) between 650 – 1050 fs, and B800 population decay ( τ 800→ ) between 10 – 50 fs. The dynamical picture that emerges is one of rapidly fluctuating LH2 eigenstates that are delocalized over multiple chromophores and undergo frequent crossing on a femtosecond timescale as a result of the atomic vibrations of the constituent chromophores. The eigenstate fluctuations arise from disorder that is driven by vibrational dynamics with multiple characteristic timescales. The scalability of our ab initio excitonic computational framework across massively parallel architectures opens up the possibility of addressing a wide range of questions, including how specific dynamical motions impact both the pathways and efficiency of electronicenergy-transfer within large supramolecular systems. |
| Databáze: | OpenAIRE |
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