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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.
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Natural Charge-Transfer Analysis: Eliminating Spurious Charge-Transfer States in Time-Dependent Density Functional Theory via Diabatization, with Application to Projection-Based Embedding
For many types of vertical excitation energies, linear-response time-dependent density functional theory (LR-TDDFT) offers a useful degree of accuracy combined with unrivaled computational efficiency, although charge-transfer excitation energies are often systematically and dramatically underestimated, especially for large systems and those that contain explicit solvent. As a result, low energy electronic spectra of solution-phase chromophores often contain tens to hundreds of spurious charge-transfer states, making LR-TDDFT needlessly expensive in bulk solution. More nefariously, intensity borrowing by the low-energy charge-transfer states can affect intensities of the valence excitations even if those excitation energies are accurate. At higher excitation energies, it is difficult to distinguish spurious CT states from genuine charge-transfer-to-solvent (CTTS) excitations. In this work, we introduce an automated diabatization scheme that enables fast and effective screening of the CTTS acceptor space in bulk solution. Our procedure introduces the concept of “natural charge-transfer orbitals”, which provide a means to isolate characteristic pairs of orbitals that are most likely to participate in a CTTS excitation. The projection of these orbitals onto solvent-centered virtual orbitals provides a criterion for defining the most important solvent molecules in a given excitation. We apply this method to analyze an ab initio molecular dynamics (MD) trajectory of I-(aq) and report the lowest-energy CTTS band in the absorption spectrum. Our results are in excellent agreement with experimental measurements for bulk I-(aq), and only one-third of the water molecules in the I-(H2O)96 simulation cell need to be described with LR-TDDFT in order to obtain excitation energies that are converged to < 0.1 eV. The tools introduced herein will improve the accuracy, efficiency, and usability of LR-TDDFT in solution-phase environments
Scientific Computation Application Partnerships in Materials and Chemical Sciences, Charge Transfer and Charge Transport in Photoactivated Systems, Developing Electron-Correlated Methods for Excited State Structure and Dynamics in the NWChem Software Suite
Charge transfer and charge transport in photoactivated systems are fundamental processes that underlie solar energy capture, solar energy conversion, and photoactivated catalysis, both organometallic and enzymatic. We developed methods, algorithms, and software tools needed for reliable treatment of the underlying physics for charge transfer and charge transport, an undertaking with broad applicability to the goals of the fundamental-interaction component of the Department of Energy Office of Basic Energy Sciences and the exascale initiative of the Office of Advanced Scientific Computing Research.
Effect of ground-state charge transfer on photoexcited charge transfer in transition metal dichalcogenide heterostructures
We report an experimental investigation on the effect of ground-state charge transfer and its induced electric field on photoexcited charge transfer in van der Waals heterostructures. Two heterostructure samples were fabricated by stacking an undoped WSe 2 monolayer with either a Nb-doped or undoped MoSe 2 monolayer. While no ground-state charge transfer is expected in the MoSe 2 /WSe 2 heterostructure, the doped holes in the MoSe 2 :Nb/WSe 2 heterostructure can transfer to WSe 2 , creating a space-charge electric field. By comparing the photoluminescence and time-resolved differential reflectance of the two heterostructures, we find that photoexcited hole transfer from MoSe 2 to WSe 2 is largely blocked by this field, whereas photoexcited electron transfer from WSe 2 to MoSe 2 is less affected. Furthermore, these results provide insight into the impact of doping on the charge-transfer performance of van der Waals heterostructures.
Charge transfer and dissociative charge transfer between rare-gas ions and molecular nitrogen.
Low collision energy charge transfer and dissociative charge transfer between rare gas ions and molecular nitrogen, measuring nitrogen ion kinetic energy distributions
Charge-Transfer Versus Charge-Transfer-Like Excitations Revisited
Criteria to assess charge-transfer (CT) and `CT-like' character of electronic excitations are examined. Time-dependent density functional theory (TDDFT) with non-hybrid, hybrid, and tuned long-range corrected (LC) functionals is compared with with coupled-cluster (CC) benchmarks. The test set includes an organic CT complex, two `push-pull' donor-acceptor chromophores, a cyanine dye, and several polycyclic aromatic hydrocarbons. Proper CT is easily identified. Excitations with significant density changes upon excitation within regions of close spatial proximity can also be diagnosed. For such excitations, the use of LC functionals in TDDFT sometimes leads to dramatic improvements of the singlet energies, similar to proper CT, which has led to the concept of `CT-like' excitations. However, `CT-like' excitations are not like charge transfer, and the improvements are not obtained for the right reasons. The triplet excitation energies are underestimated for all systems, often severely. For the `CT-like' candidates, when going from a non-hybrid to an LC functional the error in the singlet-triplet (S/T) separation changes from negative to positive, providing error compensation. For the cyanine, the S/T separation is too large with all functionals, leading to the best error compensation for non-hybrid functionals.
Ultrafast, asymmetric charge transfer and slow charge recombination in porphyrin/CNT composites demonstrated by time-domain atomistic simulation
Defect-free porphyrin/CNT hybrids can maintain long-lived charge separation; porphyrins and CNTs can be used to harvest light at different wavelengths.
Electronic structures, charge transfer, and charge order in twisted transition metal dichalcogenide bilayers
Moiré superlattices of transition metal dichalcogenide (TMD) bilayers have been shown to host correlated electronic states, which arise from the interplay of long wavelength moiré potential and long-range Coulomb interaction. Here, we theoretically investigate structural relaxation and single-particle electronic structure of twisted TMD homobilayer. From the large-scale density functional theory calculation and continuum model with layer degrees of freedom, we find that the out-of-plane gating field creates a tunable charge transfer gap at the Dirac point between the first and second moiré valence bands. We further study the charge orders at the fractional band fillings. In the flat band limit, we find from Monte Carlo simulations a series of charge-ordered insulating states at various fillings $n = \frac{1}{4}, \frac{1}{3}, \frac{1}{2}, \frac{2}{3}, 1$. Further, we predict that gating field induces a phase transition between different electron crystals at fixed filling $n = \frac{1}{2}$ or $\frac{2}{3}$. At half-filling $\textit{n} = 1$, the ground state is a Mott insulator with electronically driven ferroelectricity. This work demonstrates that TMD homobilayer provides a powerful platform for the investigation of tunable charge transfer insulator and charge orders.
Chlorophyll–carotenoid excitation energy transfer and charge transfer in Nannochloropsis oceanica for the regulation of photosynthesis
Nonphotochemical quenching (NPQ) is a proxy for photoprotective thermal dissipation processes that regulate photosynthetic light harvesting. The identification of NPQ mechanisms and their molecular or physiological triggering factors under in vivo conditions is a matter of controversy. In this work, to view chlorophyll (Chl)–zeaxanthin (Zea) excitation energy transfer (EET) and charge transfer (CT) as possible NPQ mechanisms, we performed transient absorption (TA) spectroscopy on live cells of the microalga Nannochloropsis oceanica . We gained evidence for the operation of both EET and CT quenching by observing spectral features associated with the Zea S 1 and Zea •+ excited-state absorption (ESA) signals, respectively, after Chl excitation. Knockout mutants for genes encoding either violaxanthin de-epoxidase or LHCX1 proteins exhibited strongly inhibited NPQ capabilities and lacked detectable Zea S 1 and Zea •+ ESA signals in vivo, which strongly suggests that the accumulation of Zea and active LHCX1 is essential for both EET and CT quenching in N. oceanica .
Molecular Excited States: Accurate Calculation of Relative Energies and Electronic Coupling Between Charge Transfer and Non-Charge Transfer States
We show for a series of six small donor–acceptor dyads that the energy difference between non-charge transfer (non-CT) and charge transfer (CT) excited states, as well as the squares of the electronic couplings between these states, can be predicted from first-principles using variational orbital adapted configuration interaction singles (VOA-CIS) theory. VOA-CIS correctly predicts the observed experimental trends in these values and provides quantitative accuracy roughly on par with a modern long-range corrected density functional, ωB97X. Using VOA-CIS and ωB97X, the experimental energy difference between the non-CT and CT excited states is predicted with root mean squared errors of 0.22 eV and 0.21 eV, respectively. The square of the electronic coupling between these states is predicted with root mean squared errors of 0.08 eV 2 and 0.07 eV 2 , respectively. Here, orbital optimized CIS (OO-CIS) and CIS(D), two perturbative corrections to CIS, provide a significant correction to the errant relative energies predicted by CIS, but the correction is insufficient to recover the experimentally observed trend.
Molecular Dynamics Study of the Thermodynamics of Integer Charge Transfer vs Charge-Transfer Complex
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Photoinduced Ultrafast Charge Transfer and Charge Migration in Small Gold Clusters Passivated by a Chromophoric Ligand
Not Available
Manipulation of exciton and trion quasiparticles in monolayer WS 2 via charge transfer
Charge doping in transition metal dichalcogenide is currently a subject of high importance for future electronic and optoelectronic applications. Here, we demonstrate chemical doping in the CVD-grown monolayer (1L) of WS2 by a few commonly used laboratory solvents by investigating the room temperature photoluminescence (PL). The appearance of distinct trionic emission in the PL spectra and quenched PL intensities suggests n-type doping in WS2. The temperature-dependent PL spectra of the doped 1L-WS2 reveal a significant enhancement of trions emission intensity over the excitonic emission at low temperature, indicating the stability of trion at low temperature. The temperature-dependent exciton-trion population dynamic has been modeled using the law of mass action of trion formation. These results shed light on the solution-based chemical doping in 1L-WS2 and its profound effect on the photoluminescence which is essential for the control of optical and electrical properties for optoelectronic applications.
Enhanced charge transfer by phenyl groups at a rubrene/C{sub 60} interface
Exciton dynamics at an interface between an electron donor, rubrene, and a C{sub 60} acceptor is studied by nonadiabatic quantum molecular dynamics simulation. Simulation results reveal an essential role of the phenyl groups in rubrene in increasing the charge-transfer rate by an order-of-magnitude. The atomistic mechanism of the enhanced charge transfer is found to be the amplification of aromatic breathing modes by the phenyl groups, which causes large fluctuations of electronic excitation energies. These findings provide insight into molecular structure design for efficient solar cells, while explaining recent experimental observations.
Energy transfer and charge transfer between semiconducting nanocrystals and transition metal dichalcogenide monolayers
Low-dimensional 0D/2D hybrid structures have sparked interest in interfacial carrier dynamics, like charge and energy transfer. They offer potential for electronic and optoelectronic devices such as transistors and photodetectors.
Measuring Charge Transfer between Adsorbate and Metal Surfaces
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Assembly of Surface-Confined Homochiral Helicates: Chiral Discrimination of DOPA and Unidirectional Charge Transfer
Abstract not provided