30 research outputs found
Tight-binding parameters for charge transfer along DNA
We systematically examine all the tight-binding parameters pertinent to
charge transfer along DNA. The molecular structure of the four DNA bases
(adenine, thymine, cytosine, and guanine) is investigated by using the linear
combination of atomic orbitals method with a recently introduced
parametrization. The HOMO and LUMO wavefunctions and energies of DNA bases are
discussed and then used for calculating the corresponding wavefunctions of the
two B-DNA base-pairs (adenine-thymine and guanine-cytosine). The obtained HOMO
and LUMO energies of the bases are in good agreement with available
experimental values. Our results are then used for estimating the complete set
of charge transfer parameters between neighboring bases and also between
successive base-pairs, considering all possible combinations between them, for
both electrons and holes. The calculated microscopic quantities can be used in
mesoscopic theoretical models of electron or hole transfer along the DNA double
helix, as they provide the necessary parameters for a tight-binding
phenomenological description based on the molecular overlap. We find that
usually the hopping parameters for holes are higher in magnitude compared to
the ones for electrons, which probably indicates that hole transport along DNA
is more favorable than electron transport. Our findings are also compared with
existing calculations from first principles.Comment: 15 pages, 3 figures, 7 table
Dynamical simulations of polaron transport in conjugated polymers with the inclusion of electron-electron interactions
Dynamical simulations of polaron transport in conjugated polymers in the
presence of an external time-dependent electric field have been performed
within a combined extended Hubbard model (EHM) and Su-Schrieffer-Heeger (SSH)
model. Nearly all relevant electron-phonon and electron-electron interactions
are fully taken into account by solving the time-dependent Schr\"{o}dinger
equation for the -electrons and the Newton's equation of motion for the
backbone monomer displacements by virtue of the combination of the adaptive
time-dependent density matrix renormalization group (TDDMRG) and classical
molecular dynamics (MD). We find that after a smooth turn-on of the external
electric field the polaron is accelerated at first and then moves with a nearly
constant velocity as one entity consisting of both the charge and the lattice
deformation. An ohmic region (3 mV/ 9
mV/) where the stationary velocity increases linearly with the
electric field strength is observed for the case of =2.0 eV and =1.0 eV.
The maximal velocity is well above the speed of sound. Below 3 mV/
the polaron velocity increases nonlinearly and in high electric fields with
strength 10.0 mV/ the polaron will become unstable and
dissociate. The relationship between electron-electron interaction strengths
and polaron transport is also studied in detail. We find that the the on-site
Coulomb interactions will suppress the polaron transport and small
nearest-neighbor interactions values are also not beneficial to the
polaronic motion while large values favor the polaron transport
Theoretical characterization of the absorption spectra of phenanthrene and its radical cation
The vertical absorption spectra of phenanthrene and its radical cation have been studied theoretically by means of a multiconfigurational second-order perturbation approach. Singlet-singlet transition energies and oscillator strengths, and singlet-triplet excitation energies have been studied in the absorption spectrum of phenanthrene up to 6 eV. The absorption spectrum of the phenanthrene radical cation has been computed up to 3.4 eV. The results obtained confirm previous assignments and also lead to new interpretations of the main features of the spectra of these systems
On the photophysical behaviour of 4-halo-5-phenylisoxazoles
Detailed spectral and photophysical properties of 4-halo-5-phenylisoxazoles in cyclohexane solutions are presented, including measurements of energies of lowest excited singlet and triplet states, fluorescence quantum yields, lifetimes, phosphorescence and triplet-singlet difference absorption spectra. Upon addition of ethanol, loss of vibrational structure is observed in fluorescence spectra and attributed to formation of isoxazole-ethanol aggregates. The relevance of these properties to the photochemical and thermal reactivity of these systems is discussed.http://www.sciencedirect.com/science/article/B6TFN-4H16P6W-D/1/aee849eb84047bd4755109fdbbc0c52
Ultrafast Internal Conversion of Excited Cytosine via the Lowest ππ* Electronic Singlet State
Singlet Excited-state Lifetimes of Cytosine Derivatives Measured by Femtosecond Transient Absorption¶
Multiconfigurational Second-Order Perturbation Theory Restricted Active Space (RASPT2) Method for Electronic Excited States: A Benchmark Study
IRMPD Action Spectroscopy of Alkali Metal Cation–Cytosine Complexes: Effects of Alkali Metal Cation Size on Gas Phase Conformation
Item does not contain fulltex