Competition between charge migration and charge transfer induced by nuclear motion following core ionization: Model systems and application to Li2+

2019 ◽  
Vol 151 (12) ◽  
pp. 124108
Author(s):  
Likun Yang ◽  
Jeffrey R. Reimers ◽  
Rika Kobayashi ◽  
Noel S. Hush
Keyword(s):  
Charge Transfer ◽  
Model Systems ◽  
Nuclear Motion ◽  
Charge Migration ◽  
Ionization Model

Coupled excitation energy and charge transfer dynamics in reaction centre inspired model systems

2019 ◽  
Vol 216 ◽  
pp. 72-93 ◽  
Author(s):  
Martin Richter ◽  
Benjamin P. Fingerhut
Keyword(s):  
Charge Transfer ◽  
Excitation Energy ◽  
Numerical Simulations ◽  
Model Systems ◽  
Reaction Centre ◽  
Charge Transfer Dynamics

We present numerical simulations on bacterial reaction centre (bRC) inspired model systems that utilize the recently developed MACGIC-iQUAPI method.

scholarly journals Mechanisms of triplet energy transfer across the inorganic nanocrystal/organic molecule interface

2020 ◽  
Vol 11 (1) ◽  
Author(s):  
Xiao Luo ◽  
Yaoyao Han ◽  
Zongwei Chen ◽  
Yulu Li ◽  
Guijie Liang ◽  
...  
Keyword(s):  
Energy Transfer ◽  
Charge Transfer ◽  
Organic Molecule ◽  
Transient Absorption ◽  
High Energy ◽  
Model Systems ◽  
Trap States ◽  
Triplet Energy ◽  
Surface Trap ◽  
Triplet Energy Transfer

AbstractThe mechanisms of triplet energy transfer across the inorganic nanocrystal/organic molecule interface remain poorly understood. Many seemingly contradictory results have been reported, mainly because of the complicated trap states characteristic of inorganic semiconductors and the ill-defined relative energetics between semiconductors and molecules used in these studies. Here we clarify the transfer mechanisms by performing combined transient absorption and photoluminescence measurements, both with sub-picosecond time resolution, on model systems comprising lead halide perovskite nanocrystals with very low surface trap densities as the triplet donor and polyacenes which either favour or prohibit charge transfer as the triplet acceptors. Hole transfer from nanocrystals to tetracene is energetically favoured, and hence triplet transfer proceeds via a charge separated state. In contrast, charge transfer to naphthalene is energetically unfavourable and spectroscopy shows direct triplet transfer from nanocrystals to naphthalene; nonetheless, this “direct” process could also be mediated by a high-energy, virtual charge-transfer state.

scholarly journals Coupled electron-nuclear dynamics: Charge migration and charge transfer initiated near a conical intersection

2013 ◽  
Vol 139 (4) ◽  
pp. 044110 ◽  
Author(s):  
David Mendive-Tapia ◽  
Morgane Vacher ◽  
Michael J. Bearpark ◽  
Michael A. Robb
Keyword(s):  
Charge Transfer ◽  
Conical Intersection ◽  
Charge Migration ◽  
Nuclear Dynamics

scholarly journals Charge migration and charge transfer in molecular systems

2017 ◽  
Vol 4 (6) ◽  
pp. 061508 ◽  
Author(s):  
Hans Jakob Wörner ◽  
Christopher A. Arrell ◽  
Natalie Banerji ◽  
Andrea Cannizzo ◽  
Majed Chergui ◽  
...  
Keyword(s):  
Charge Transfer ◽  
Charge Migration ◽  
Molecular Systems

scholarly journals Applications of model systems to explore exchange-correlation effects in density-functional theory

2020 ◽  
Author(s):  
◽  
Edward A. III Pluhar
Keyword(s):  
Charge Transfer ◽  
Magnetic Fields ◽  
Density Functional ◽  
Model System ◽  
Orbit Coupling ◽  
Model Systems ◽  
Spin Orbit Coupling ◽  
Spin Orbit ◽  
Electron Dynamics ◽  
Functional Theory

Density-functional theory (DFT), in its various forms, has become a near ubiquitous form of theoretical research used to benchmark and prototype solutions to many finite and extended state system. This is largely because DFT can both capture the rich physics that is present in these electronic systems, while remaining computationally cost-effective and interpretable. However, DFT also has the requirement that the density functional being used to iteratively converge towards a solution must be accurate and correct. While on the surface such a stipulation seems benign, in practice the density functionals can be overwhelmingly complex and error can be introduced that comes from either the density functional that is chosen or the approximations used to make a system more calculationally tenable. In this work, our focus is on the use of model systems to calculate and determine the usefulness and shortcomings of DFT. By simplifying the underlying system, while also retaining enough physical quantities from real systems, we can focus on how the approximations affect the outcomes that are produced. To begin, we show that charge-transfer dynamics can be described in unique and enlightening ways through the use of the particle-hole map (PHM). Using a one-dimensional, multi-well system, we effectively demonstrate how interesting electron dynamics can be uncovered by applying unitary transformations to the wavefunctions. By spatially localizing the electronic wavefunctions through the Foster-Boys method, which is analogous to Wannier localization in extended systems, the intermediating components of charge transfer systems can be examined to determine their effect on the system-at-large. From the simple one-dimensional system, we could quickly infer real molecular systems that could potentially be examined using the same method to surmise the role charge-transfer intermediaries play in such systems as organic photovoltaics. Beyond electron dynamics, the role of exchange-correlation (xc) scalar potentials and magnetic fields that are features of noncollinear spin Kohn-Sham (KS) and DFT was explored by comparing the exact Schroedinger solution to the KS and DFT approximations. By extending the Hubbard model to four sites, we can both solve the system exactly, while allowing for on-site and nearest-neighbor interactions. We were able to obtain benchmark solutions across a wide range of interaction strengths, determining that there are regimes where the xc magnetic fields play an increasingly larger role as the system becomes more correlated. In fact, there is a regime where the xc magnetic fields become larger than the external magnetic fields that are applied on the system. Through the model system, we could additionally compare the exact solutions against the approximated xc functionals and demonstrate that the weakly correlated regime can be adequately described by the xc functional approximations common to many real-systems. Moving beyond steady state observations, we can also describe time-dependent electron dynamics through real-time TDDFT and use a model system to compare the time-evolution of the exact and KS solutions. By allowing the xc potentials to propagate in real time, we could explore the role the xc torques played during the evolution of a triangular lattice under an applied, time-varying magnetic field. Additionally, by controlling the spin-orbit coupling present in the small model system, we determined that the spin orbit coupling plays a substantial role in keeping the spins more closely aligned with the exact system. In part, this was due to the spin-orbit coupling serving as a time-varying magnetic field, which tended to be larger than the xc potentials that were also present. The trimer can also be quickly and easily expanded with the added spin-orbit coupling and compared to real model systems through computational physics software, such as Octopus.

Modulating charge migration in photoredox organic transformation via exquisite interface engineering

2020 ◽  
Vol 8 (17) ◽  
pp. 8360-8375
Author(s):  
Shuai Xu ◽  
Ming-Hui Huang ◽  
Tao Li ◽  
Zhi-Quan Wei ◽  
Xin Lin ◽  
...  
Keyword(s):  
Charge Transfer ◽  
Visible Light ◽  
Visible Light Irradiation ◽  
High Efficiency ◽  
Light Irradiation ◽  
Interface Engineering ◽  
Organic Transformations ◽  
Charge Migration ◽  
First Time

An ionic polyelectrolyte was for the first time revealed to serve as an unexpected high-efficiency cascade charge transfer mediator toward versatile photoredox organic transformations under visible light irradiation.

Excitation Dynamics and Losses in Solution Processed Disordered Semiconductors

2021 ◽  
Author(s):  
◽  
Nasim Zarrabi
Keyword(s):  
Solar Cells ◽  
Charge Transfer ◽  
Charge Carrier ◽  
Organic Semiconductor ◽  
Organic Solar Cells ◽  
Impurity Content ◽  
Dielectric Constants ◽  
Embodied Energy ◽  
Model Systems ◽  
Trap States

From a technological point of view, organic semiconductor-based devices are of significant interest due to their light weight, ease of processability, conformal flexibility and potentially low cost and low embodied energy pro-duction. Motivated by these quite unique selling points, the performance of organic semiconductors has been a subject of multi-disciplinary study for more than 60 years with steady progress in applications such as solar cells, transistors, light emitting diodes and various sensors. One of the main characteristics that governs the performance of organic semiconduc-tors is their low dielectric constants, meaning they are excitonic at room temperature. A second main feature that dictates the charge carrier recom-bination and transport properties is the disordered nature of these semicon-ductors causing low charge carrier mobilities. The work described in this thesis focuses on these defining elements, and particularly their implications on photovoltaic devices. The discussion will start with a review into the main electro-optical phenomena in organic solar cells. Subsequently, a new method is presented for measuring exciton diffusion lengths based upon a low-quencher-content device structure. An anomalously large quenching volume is observed that can be assigned to long-range exciton delocaliza-tion prior to thermalization. These ultra-low-impurity content organic so-lar cells are also very useful as model systems to study and engineer trap states. Using this approach, it is found that mid-gap trap states are a universal feature in organic semiconductor donor-acceptor blends and un-expectedly contribute to charge generation and recombination. This has a profound impact on the thermodynamic limit of organic photovoltaic de-vices. Having demonstrated this important new insight it is further shown that a definitive link exists between a reduced recombination rate compared to the Langevin rate in some exceptional, high performance material sys-tems and a significant increase in the dissociation rate of charge transfer states upon post-processing of the active layer. In sum, the work presented in this thesis delivers important new insight as to the underlying dynamics of exciton generation and diffusion, charge transfer state dissociation, and indeed the ultimate fate of photogenerated free carriers.

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