884 research outputs found
Dynamical simulations of charged soliton transport in conjugated polymers with the inclusion of electron-electron interactions
We present numerical studies of the transport dynamics of a charged soliton
in conjugated polymers under the influence of an external time-dependent
electric field. All relevant electron-phonon and electron-electron interactions
are nearly fully taken into account by simulating the monomer displacements
with classical molecular dynamics (MD) and evolving the wavefunction for the
electrons by virtue of the adaptive time-dependent density matrix
renormalization group (TDDMRG) simultaneously and nonadiabatically. It is found
that after a smooth turn-on of the external electric field the charged soliton
is accelerated at first up to a stationary constant velocity as one entity
consisting of both the charge and the lattice deformation. An ohmic region (6
mV/ 12 mV/) where the stationary
velocity increases linearly with the electric field strength is observed. The
relationship between electron-electron interactions and charged soliton
transport is also investigated in detail. We find that the dependence of the
stationary velocity of a charged soliton on the on-site Coulomb interactions
and the nearest-neighbor interactions is due to the extent of
delocalization of the charged soliton defect.Comment: 25 pages, 15 figure
Modulating the exciton dissociation rate by up to more than two orders of magnitude by controlling the alignment of LUMO + 1 in organic photovoltaics
Efficient organic solar cells require a high yield of exciton dissociation. Herein we investigate the possibility of having more than one charge-transfer (CT) state below the first optically bright Frenkel exciton state (FE) for common molecular donor (D)/acceptor (A) pairs and the role of the second-lowest CT state (CT2) in the exciton dissociation process. This situation, previously explored only for fullerene acceptors, is shown to be rather common for other D/A pairs. By considering a phenomenological model of a large aggregate, we reveal that the position of CT2 can remarkably modulate the exciton dissociation rate by up to more than two orders of magnitude. Thus, controlling the alignment of CT2 is suggested as a promising rule for designing new D/A heterojunctions
Trends in the electronic and geometric structure of non-fullerene based acceptors for organic solar cells
We constructed a database of 80 high performing non-fullerene electron acceptors and studied the common electronic and geometric properties in search of unifying design rules. We discovered that, without exception, all high performing materials are characterized by very low gap between LUMO and LUMO+1 orbitals, a feature that is consistent with microscopic models and seems to be true for all classes of compounds considered. We also confirmed that non-planarity of the acceptor is beneficial but not for all classes of acceptors. We suggested that by building similar databases and keeping it up to date it will be possible to identify statistically meaningful structure-property relations
Mechanochemical Coupling in the Myosin Motor Domain. I. Insights from Equilibrium Active-Site Simulations
Although the major structural transitions in molecular motors are often argued to couple to the binding of Adenosine triphosphate (ATP), the recovery stroke in the conventional myosin has been shown to be dependent on the hydrolysis of ATP. To obtain a clearer mechanistic picture for such “mechanochemical coupling” in myosin, equilibrium active-site simulations with explicit solvent have been carried out to probe the behavior of the motor domain as functions of the nucleotide chemical state and conformation of the converter/relay helix. In conjunction with previous studies of ATP hydrolysis with different active-site conformations and normal mode analysis of structural flexibility, the results help establish an energetics-based framework for understanding the mechanochemical coupling. It is proposed that the activation of hydrolysis does not require the rotation of the lever arm per se, but the two processes are tightly coordinated because both strongly couple to the open/close transition of the active site. The underlying picture involves shifts in the dominant population of different structural motifs as a consequence of changes elsewhere in the motor domain. The contribution of this work and the accompanying paper [36] is to propose the actual mechanism behind these “population shifts” and residues that play important roles in the process. It is suggested that structural flexibilities at both the small and large scales inherent to the motor domain make it possible to implement tight couplings between different structural motifs while maintaining small free-energy drops for processes that occur in the detached states, which is likely a feature shared among many molecular motors. The significantly different flexibility of the active site in different X-ray structures with variable level arm orientations supports the notation that external force sensed by the lever arm may transmit into the active site and influence the chemical steps (nucleotide hydrolysis and/or binding)
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