474 research outputs found
Ab initio calculation of interatomic decay rates of excited doubly ionized states in clusters
Coulombic Energy Transfer and Triple Ionization in Clusters
Using neon and its dimer as a specific example, it is shown that excited
Auger decay channels that are electronically stable in the isolated monomer can
relax in a cluster by electron emission. The decay mechanism, leading to the
formation of a tricationic cluster, is based on an efficient energy-transfer
process from the excited, dicationic monomer to a neighbor. The decay is
ultrafast and expected to be relevant to numerous physical phenomena involving
core holes in clusters and other forms of spatially extended atomic and
molecular matter.Comment: 5 pages, 1 figure, to be published in PR
Ab initio Green's function formalism for band structures
Using the Green's function formalism, an ab initio theory for band structures
of crystals is derived starting from the Hartree-Fock approximation. It is
based on the algebraic diagrammatic construction scheme for the self-energy
which is formulated for crystal orbitals (CO-ADC). In this approach, the poles
of the Green's function are determined by solving a suitable Hermitian
eigenvalue problem. The method is not only applicable to the outer valence and
conduction bands, it is also stable for inner valence bands where strong
electron correlations are effective. The key to the proposed scheme is to
evaluate the self-energy in terms of Wannier orbitals before transforming it to
a crystal momentum representation. Exploiting the fact that electron
correlations are mainly local, one can truncate the lattice summations by an
appropriate configuration selection scheme. This yields a flat configuration
space; i.e., its size scales only linearly with the number of atoms per unit
cell for large systems and, under certain conditions, the computational effort
to determine band structures also scales linearly. As a first application of
the new formalism, a lithium fluoride crystal has been chosen. A minimal basis
set description is studied, and a satisfactory agreement with previous
theoretical and experimental results for the fundamental band gap and the width
of the F 2p valence band complex is obtained.Comment: 20 pages, 3 figures, 1 table, RevTeX4, new section on lithium
fluorid
An Event Structure Model for Probabilistic Concurrent Kleene Algebra
We give a new true-concurrent model for probabilistic concurrent Kleene
algebra. The model is based on probabilistic event structures, which combines
ideas from Katoen's work on probabilistic concurrency and Varacca's
probabilistic prime event structures. The event structures are compared with a
true-concurrent version of Segala's probabilistic simulation. Finally, the
algebraic properties of the model are summarised to the extent that they can be
used to derive techniques such as probabilistic rely/guarantee inference rules.Comment: Submitted and accepted for LPAR19 (2013
Competition between decay and dissociation of core-excited OCS studied by X-ray scattering
We show the first evidence of dissociation during resonant inelastic soft
X-ray scattering. Carbon and oxygen K-shell and sulfur L-shell resonant and
non-resonant X-ray emission spectra were measured using monochromatic
synchrotron radiation for excitation and ionization. After sulfur, L2,3 ->
{\pi}*, {\sigma}* excitation, atomic lines are observed in the emission spectra
as a consequence of competition between de-excitation and dissociation. In
contrast the carbon and oxygen spectra show weaker line shape variations and no
atomic lines. The spectra are compared to results from ab initio calculations
and the discussion of the dissociation paths is based on calculated potential
energy surfaces and atomic transition energies.Comment: 12 pages, 6 pictures, 2 tables,
http://link.aps.org/doi/10.1103/PhysRevA.59.428
Soft lubrication: the elastohydrodynamics of non-conforming and conforming contacts
We study the lubrication of fluid-immersed soft interfaces and show that
elastic deformation couples tangential and normal forces and thus generates
lift. We consider materials that deform easily, due to either geometry (e.g. a
shell) or constitutive properties (e.g. a gel or a rubber), so that the effects
of pressure and temperature on the fluid properties may be neglected. Four
different system geometries are considered: a rigid cylinder moving parallel to
a soft layer coating a rigid substrate; a soft cylinder moving parallel to a
rigid substrate; a cylindrical shell moving parallel to a rigid substrate; and
finally a cylindrical conforming journal bearing coated with a thin soft layer.
In addition, for the particular case of a soft layer coating a rigid substrate
we consider both elastic and poroelastic material responses. For all these
cases we find the same generic behavior: there is an optimal combination of
geometric and material parameters that maximizes the dimensionless normal force
as a function of the softness parameter = hydrodynamic pressure/elastic
stiffness = surface deflection/gap thickness which characterizes the
fluid-induced deformation of the interface. The corresponding cases for a
spherical slider are treated using scaling concepts.Comment: 61 pages, 20 figures, 2 tables, submitted to Physics of Fluid
Vibronic coupling and core-hole localization in K-shell excitations of ethylene
A new high-resolution measurement of the C 1s near-edge photoabsorption spectrum of the ethylene molecule is reported. An analysis of the vibrational structure in the C 1s-Ď€* band indicates strong excitation of non-totally-symmetry modes and the importance of vibronic coupling. The latter phenomenon provides a mechanism for core-hole localization in the final state
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