Untangling Excitonic Energy Transfer for the LHC

Untangling Excitonic Energy Transfer for the LHC-II complex
from Full First-Principles Calculations.
Joaquim Jornet-Somoza1, Joseba Alberdi-Rodríguez2, Bruce Milne3, Xavier
Andrade4, Miguel A. L. Marques5, Fernando Nogueira3, Micael J. T. Oliveira6,
Angel Rubio2
1) Universitat de Barcelona, Martí i Franquès 1, 08028 Barcelona, Spain
2) Nano-Bio Spectroscopy group and ETSF Scientific Development Centre,
Department of Materials Physics, University of the Basque Country, CFM CSICUPV/EHU-MPC and DIPC, Tolosa Hiribidea 72, E-20018 Donostia-San Sebastián,
3) CFisUC, Department of Physics, University of Coimbra, Rua Larga, 3004–516
Coimbra, Portugal.
4) Lawrence Livermore National Laboratory, Livermore, CA 94550, United States
5) Institut für Physik, Martin-Luther-Universität Halle-Wittenberg, D-06099 Halle,
6) Department of Physics, University of Liège, B-4000, Liège, Belgium
Corresponding author: Joaquim Jornet ([email protected])
The current increase in energy demands across the world makes fossil-fuel based
energy resources unsustainable. Solar energy conversion is one alternative to produce
green renewable energy. However, the efficiency of current organic photovoltaic cells is
still low (<10%) compared with natural biological systems (~100%). A deeper
understanding of the mechanism that governs the energy transfer inside natural lightharvesting systems will be essential to design highly efficient and bio-inspired
devices. In this work we present a full first–principles calculations within the framework
of real–space time–dependent density functional theory (TD-DFT) for the complete
chlorophyll (Chl) network (~7000 atoms) of the light–harvesting complex from green
plants, LHC–II. A local analysis method of the time dependent densities ( (t))
developed for this work has made possible quantum–mechanical studies of the optical
response of individual chlorophyll molecules subject to the influence of the remainder
of the chromophore network. The site-specific alterations in chlorophyll excitation
energies support the existence of distinct energy transfer pathways within the LHC-II
complex. We propose a new treatment of the (t) that enables the calculation of the
transition densities for big systems, and the exciton energy transfer inside chlorophyll
network going beyond Förster’s model.