APS March Meeting 2017
Volume 62, Number 4
Monday–Friday, March 13–17, 2017;
New Orleans, Louisiana
Session E25: Chemical Physics of Multichromophores II
8:00 AM–11:00 AM,
Tuesday, March 14, 2017
Room: 288
Sponsoring
Unit:
DCP
Chair: Tim Berkelbach, University of Chicago
Abstract ID: BAPS.2017.MAR.E25.7
Abstract: E25.00007 : Atomistic absorption spectra and non-adiabatic dynamics of the LH2 complex with a GPU-accelerated \textit{ab initio} exciton model
10:00 AM–10:36 AM
Preview Abstract
Abstract
Author:
David Glowacki
(University of Bristol)
Recently, we outlined an efficient multi-tiered parallel excitonic framework
that utilizes time dependent density functional theory (TDDFT) to calculate
ground/excited state energies and gradients of large supramolecular
complexes in atomistic detail. In this paper, we apply our \textit{ab initio }exciton framework
to the 27 coupled bacteriocholorophyll-a chromophores which make up the LH2
complex, using it to compute linear absorption spectra and short-time,
on-the-fly nonadiabatic surface-hopping (SH) dynamics of electronically
excited LH2. Our \textit{ab initio} exciton model includes two key parameters whose values are
determined by fitting to experiment: d, which is added to the diagonal
elements, corrects for the error in TDDFT vertical excitation energies on a
single chromophore; and e, which occurs on the off-diagonal matrix elements,
describes the average dielectric screening of the inter-chromophore
transition-dipole coupling. Using snapshots obtained from equilibrium
molecular dynamics simulations (MD) of LH2, best-fit values of both d and e
were obtained by fitting to the thermally broadened experimental absorption
spectrum within the Frank-Condon approximation, providing a linear
absorption spectrum that agrees reasonably well with the experimental
observations. We follow the nonadiabatic dynamics using surface hopping to
construct time-resolved visualizations of the EET dynamics in the
sub-picosecond regime following photoexcitation. This provides some
qualitative insight into the excitonic energy transfer (EET) that results
from atomically resolved vibrational fluctuations of the chromophores. The
dynamical picture that emerges is one of rapidly fluctuating eigenstates
that are delocalized over multiple chromophores and undergo frequent
crossing on a femtosecond timescale as a result of the underlying
chromophore vibrational dynamics. The eigenstate fluctuations arise from
disorder in both the diagonal chromophore site energies and the off-diagonal
inter-chromophore couplings. The scalability of our 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 electronic
energy-transfer within large supramolecular systems.
To cite this abstract, use the following reference: http://meetings.aps.org/link/BAPS.2017.MAR.E25.7