196,171 research outputs found
Unveiling the Role of Hot Charge-Transfer States in Molecular Aggregates via Nonadiabatic Dynamics
No full textExciton dynamics governs energy transfer and charge generation in organic functional materials. We investigate high-energy nonadiabatic excited-state dynamics for a bithiophene dimer to describe time-dependent excitonic effects in molecular aggregates. We show that the lowest excited states are populated on the subpicosecond time scale. These states are localized and unproductive in terms of charge separation. Productive high-energy charge-transfer (CT) states are populated within 50 fs during exciton deactivation, but they are short-lived (similar to 100 fs) and quickly transfer their population to lower states. Our simulations offer molecular-level insights into ultrafast photoinduced charge separation potentially triggered by hot CT states in solid-state organic materials. Design rules are suggested to increase hot exciton lifetimes, favoring the population of CT states as gateways for direct charge generation. These rules may boost the CT quantum yield by depleting unproductive recombination channels
Modeling ultrafast exciton deactivation in oligothiophenes via nonadiabatic dynamics
No full textUltrafast excited-state processes play a key role in organic electronics and photovoltaics, governing the way of how excitons can relax and separate. Through the use of nonadiabatic excited-state dynamics, relaxation processes were investigated at the sub-picosecond timescale in thiophene and oligothiophenes (nT, n = 2, 3, 4), prototype oligomers for efficient pi-electron conjugated polymers adopted in photovoltaics. For thiophene, TDDFT and TDA nonadiabatic excited-state dynamics revealed ultrafast nonradiative relaxation processes through ring opening and ring puckering, bringing the system to an S-1/S-0 conical intersection seam. The computed relaxation time is 110 fs, matching well the experimental one (similar to 105 fs). In oligothiophenes (n = 2-4), high-energy (hot) excitations were considered. Exciton relaxation through the manifold of excited states to the lowest excited state is predicted to occur within similar to 150-200 fs, involving bond stretching, ring puckering, and torsional oscillations. For the longer oligomer (4T), the ultrafast relaxation process leads to exciton localization over three thiophene rings in 150 fs. These data agree with the self-localization mechanism (similar to 100-200 fs) observed for poly(3-hexylthiophene) (P3HT) and shed light on the complex exciton relaxation dynamics occurring in pi-conjugated oligomers of potential interest for optoelectronic applications
Trajectory Surface Hopping for a Polarizable Embedding QM/MM Formulation
No full textWe present the implementation of trajectory surface-hopping nonadiabatic dynamics for a polarizable embedding QM/MM formulation. Time-dependent density functional theory was used at the quantum mechanical level of theory, whereas the molecular mechanics description involved the polarizable AMOEBA force field. This implementation has been obtained by integrating the surface-hopping program Newton-X NS with an interface between the Gaussian 16 and the Tinker suites of codes to calculate QM/AMOEBA energies and forces. The implementation has been tested on a photoinduced electron-driven proton-transfer reaction involving pyrimidine and a hydrogen-bonded water surrounded by a small cluster of water molecules and within a large water droplet
Semiempirical molecular dynamics investigation of the excited state lifetime of ethylene
No full textSemiempirical molecular dynamics with surface hopping was employed to investigate the lifetime of excited states of ethylene. Based on previous ab initio multireference configuration interaction results, a complete reparametrization of the AM1 semiempirical parameters was performed. Depending on the initial vertical excitation energy, lifetimes from 105 to 139 fs were found for the V-state decay. Comparison to the pump–probe experiments was performed in order to explain the large differences between the theoretically and experimentally obtained lifetimes. The results show that probe energies of at least 7.4 eV should be employed to ionize the system for geometries close to the conical intersections
Newton-X: a surface-hopping program for nonadiabatic molecular dynamics
No full textThe Newton-X program is a general-purpose program package for excited-state molecular dynamics, including nonadiabatic methods. Its modular design allows Newton-X to be easily linked to any quantum-chemistry package that can provide excited-state energy gradients. At the current version, Newton-X can perform nonadiabatic dynamics using Columbus, Turbomole, Gaussian, and Gamess program packages with multireference configuration interaction, multiconfigurational self-consistent field, time-dependent density functional theory, and other methods. Nonadiabatic dynamics simulations with a hybrid combination of methods, such as Quantum-Mechanics/Molecular-Mechanics, are also possible. Moreover, Newton-X can be used for the simulation of absorption and emission spectra. The code is distributed free of charge for noncommercial and nonprofit uses at www.newtonx.org
Research data underlying the manuscript "Classification of Doubly Excited Molecular Electronic States" by M. T. do Casal, J. M. Toldo, M. Barbatti and F. Plasser.
No full textResearch data underlying the manuscript "Classification of Doubly Excited Molecular Electronic States" by M. T. do Casal, J. M. Toldo, M. Barbatti and F. Plasser.
Content: Single point calculations were performed on the systems below. Each molecule folder contains subfolders with inputs and outputs at the electronic structure level indicated below.
1. Formaldehyde Dimer
a. ADC(3)
2. Polyenes
a. DFT/MRCI
b. ADC(3)
c. MRCISD
d. TDDFT
3. Cycloaddtion of Ethylene
a. MRCISD
4. DPP Dimer
a. DFT/MRCI
5. Tetracene Dimer
a. DFT/MRCI
6. Tetrazine
a. DFT/MRCI
7. bis-Thiophene
a. DFT/MRCIa singlets
DFT/MRCI folders contain the following files:
control: TURBOMOLE's input file
coord: Input geometry for TURBOMOLE and DFT/MRCI
mrci.inp: Input file for DFT/MRCI
run_dftci.inp: Input file for the driver interfacing TURBOMOLE and DFT/MRCI
mrci.sum: Summary of DFT/MRCI calculations
ADC(3) folders contain the following files:
qchem-monomer.in: Q-Chem input file
qchem.out: Q-Chem output file
libwfa_summ.txt: Output file summarising excited state properties
MRCISD folders contain:
INPUT directory: All necessary input files for COLUMBUS
LISTINGS: All output files generated by COLUMBUS
TDDFT folders contain:
coord.qchem: Input geometry for Q-Chem
qchem.in: Q-Chem input file
qchem.out: Q-Chem output file
libwfa_summ.txt: Output file summarising excited state properties
Output files for TheoDORE summarising excited state properties are also provided:
tden_summ.txt: Output file from TheoDORE for the transition density matrix analysis
sden_summ.txt.: Output file from TheoDORE for the state density matrix analysis.
All results used for plotting are compiled in two datasets: cycloaddition.csv and polyenes.csv.</p
Surface hopping dynamics using a locally diabatic formalism: charge transfer in the ethylene dimer cation and excited state dynamics in the 2-pyridone dimer.
No full textIn this work, the advantages of a locally diabatic propagation of the electronic wave function in surface
hopping dynamics proceeding on adiabatic surfaces are presented providing very stable results
even in challenging cases of highly peaked nonadiabatic interactions. The method was applied to the simulation of transport phenomena in the stacked ethylene dimer radical cation and the hydrogen bonded 2-pyridone dimer. Systematic tests showed the reliability of the method, in situations where
standard methods relying on an adiabatic propagation of the wave function and explicit calculation
of the nonadiabatic coupling terms exhibited significant numerical instabilities. Investigations of the
ethylene dimer radical cation with an intermolecular distance of 7.0 angstrom provided a quantitative description of diabatic charge trapping. For the 2-pyidone dimer, a complex dynamics was obtained:
a very fast (<10 fs) initial S2/S1 internal conversion; subsequent excitation energy transfers with a
characteristic time of 207 fs; and the occurrence of proton coupled electron transfer (PCET) in 26%
of the trajectories. The computed characteristic excitation energy transfer time of 207 fs is in satisfactory
agreement with the experimental value of 318 fs derived from the vibronic exciton splittings in a
monodeuterated 2-pyridone dimer complex. The importance of nonadiabatic coupling for the PCET related to the electron transfer was demonstrated by the dynamics simulations
Dr. Duane M. Jackson, Morehouse College, July 2011
No full textThis video is a conversation with Dr. Duane M. Jackson. Dr. Jackson talks about his paper, "Recall and the Serial Position Effect: The Role of Primacy and Recency on Accounting Students' Performance." Jackie Daniel, AUC Woodruff Library, is the interviewer
Conformational dynamics of the pyrene excimer
No full textThe conformational dynamics of the pyrene excimer play a critical role in its unique fluorescence properties. Yet, the influence of multiple local minima on its excited-state behavior remains underexplored. Using a combination of time-dependent density functional theory (TD-DFT) and unsupervised machine learning analysis, we have identified and characterized a diverse set of stable excimer geometries in the first excited state. Our analysis reveals that rapid structural reorganization towards the most stable stacked-twisted conformer dominates the excimer's photophysics, outcompeting radiative relaxation. This conformer, which is primarily responsible for the characteristic red-shifted, structureless fluorescence emission, reconciles experimental observations of long fluorescence lifetimes and emission profiles. These findings provide new insights into the excited-state dynamics of excimers. They may inform the design of excimer-based materials in fields ranging from organic electronics to molecular sensing
"Reflections on the subject of Emigration from Europe with a view to Settlement in the United States" By M. Carey.
No full text"Reflections on the subject of Emigration from Europe with a view to Settlement in the United States: containing bried sketches of the moral and political character of those states.
By M. Carey, member of the American philosophical, and of the American Antiquarian Society, and author of The Olive Branch, Cindiciae Hibernicae, essays on banking, on political economy, and on internal improvement.
To which are now added the English editor's comments on the subject; together with Important Advice to Emigrants, and Cautions Against Impositions Practiced in the Outports
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