9,150 research outputs found
Book Review of David Lester, Making Sense of Suicide: An In-depth Look at Why People Kill Themselves (The Charles Press 1997)
Review of the book David Lester, Making Sense of Suicide: An In-depth Look at Why People Kill Themselves (The Charles Press 1997). Preface, bibliographical references, index. ISBN 0-914783-82-3. [208 pp. Paper $22.95. P.O. Box 15715, Philadelphia, PA 19103.
Computational design of metal-supported molecular switches: Transient ion formation during light- and electron-induced isomerisation of azobenzene
In molecular nanotechnology, a single molecule is envisioned to act as the
basic building block of electronic devices. Such devices may be of special
interest for organic photovoltaics, data storage, and smart materials. However,
more often than not the molecular function is quenched upon contact with a
conducting support. Trial-and-error-based decoupling strategies via molecular
functionalisation and change of substrate have in many instances proven to
yield unpredictable results. The adsorbate-substrate interactions that govern
the function can be understood with the help of first-principles simulation.
Employing dispersion-corrected Density-Functional Theory (DFT) and linear
expansion Delta-Self-Consistent-Field DFT, the electronic structure of a
prototypical surface-adsorbed functional molecule, namely azobenzene adsorbed
to (111) single crystal facets of copper, silver and gold, is investigated and
the main reasons for the loss or survival of the switching function upon
adsorption are identified. The light-induced switching ability of a
functionalised derivative of azobenzene on Au(111) and azobenzene on Ag(111)
and Au(111) is assessed based on the excited-state potential energy landscapes
of their transient molecular ions, which are believed to be the main
intermediates of the experimentally observed isomerisation reaction. We provide
a rationalisation of the experimentally observed function or lack thereof that
connects to the underlying chemistry of the metal-surface interaction and
provides insights into general design strategies for complex light-driven
reactions at metal surfaces.Comment: 14 pages, 5 figures, submitted to J. Phys. Condens. Matte
Bistability loss as key feature in azobenzene (non-)switching on metal surfaces
Coinage metal adsorbed azobenzene is investigated as prototypical molecular
switch. It is shown that switching capabilities are not just lost due to
excited state quenching, but already due to changes in the ground state
energetics. Electron demanding coadsorbates are suggested as strategy to regain
the switching function.Comment: 8 pages, 3 figure
Assessing computationally efficient isomerization dynamics: Delta-SCF density-functional theory study of azobenzene molecular switching
We present a detailed comparison of the S0, S1 (n -> \pi*) and S2 (\pi ->
\pi*) potential energy surfaces (PESs) of the prototypical molecular switch
azobenzene as obtained by Delta-self-consistent-field (Delta-SCF)
Density-Functional Theory (DFT), time-dependent DFT (TD-DFT) and approximate
Coupled Cluster Singles and Doubles (RI-CC2). All three methods unanimously
agree in terms of the PES topologies, which are furthermore fully consistent
with existing experimental data concerning the photo-isomerization mechanism.
In particular, sum-method corrected Delta-SCF and TD-DFT yield very similar
results for S1 and S2, when based on the same ground-state exchange-correlation
(xc) functional. While these techniques yield the correct PES topology already
on the level of semi-local xc functionals, reliable absolute excitation
energies as compared to RI-CC2 or experiment require an xc treatment on the
level of long-range corrected hybrids. Nevertheless, particularly the
robustness of Delta-SCF with respect to state crossings as well as its
numerical efficiency suggest this approach as a promising route to dynamical
studies of larger azobenzene-containing systems.Comment: 25 pages, 6 figure
The two-proton shell gap in Sn isotopes
We present an analysis of two-proton shell gaps in Sn isotopes. As the
theoretical tool we use self-consistent mean-field models, namely the
relativistic mean-field model and the Skyrme-Hartree-Fock approach, both with
two different pairing forces, a delta interaction (DI) model and a
density-dependent delta interaction (DDDI). We investigate the influence of
nuclear deformation as well as collective correlations and find that both
effects contribute significantly. Moreover, we find a further significant
dependence on the pairing force used. The inclusion of deformation plus
correlation effects and the use of DDDI pairing provides agreement with the
data.Comment: gzipped tar archiv containing LaTeX source, bibliography file
(*.bbl), all figures as *.eps, and the style file
The Skyrme Interaction in finite nuclei and nuclear matter
Self-consistent mean-field models are a powerful tool in the investigation of
nuclear structure and low-energy dynamics. They are based on effective
energy-density functionals, often formulated in terms of effective
density-dependent nucleon-nucleon interactions. The free parameters of the
functional are adjusted to empirical data. A proper choice of these parameters
requires a comprehensive set of constraints covering experimental data on
finite nuclei, concerning static as well as dynamical properties, empirical
characteristics of nuclear matter, and observational information on
nucleosynthesis, neutron stars and supernovae. This work aims at a
comprehensive survey of the performance of one of the most successful
non-relativistic self-consistent method, the Skyrme-Hartree-Fock model (SHF),
with respect to these constraints. A full description of the Skyrme functional
is given and its relation to other effective interactions is discussed. The
validity of the application of SHF far from stability and in dense environments
beyond the nuclear saturation density is critically assessed. The use of SHF in
models extended beyond the mean field approximation by including some
correlations is discussed. Finally, future prospects for further development of
SHF towards a more consistent application of the existing and promisingly newly
developing constraints are outlined.Comment: 71 pages, 22 figures. Accepted for publication in Prog.Part.Nucl.Phy
Misfits in Skyrme-Hartree-Fock
We address very briefly five critical points in the context of the
Skyrme-Hartree-Fock (SHF) scheme: 1) the impossibility to consider it as an
interaction, 2) a possible inconsistency of correlation corrections as, e.g.,
the center-of-mass correction, 3) problems to describe the giant dipole
resonance (GDR) simultaneously in light and heavy nuclei, 4) deficiencies in
the extrapolation of binding energies to super-heavy elements (SHE), and 5) a
yet inappropriate trend in fission life-times when going to the heaviest SHE.
While the first two points have more a formal bias, the other three points have
practical implications and wait for solution.Comment: 9 pages, 4 figure
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