2,372 research outputs found
Relativistic central--field Green's functions for the RATIP package
From perturbation theory, Green's functions are known for providing a simple
and convenient access to the (complete) spectrum of atoms and ions. Having
these functions available, they may help carry out perturbation expansions to
any order beyond the first one. For most realistic potentials, however, the
Green's functions need to be calculated numerically since an analytic form is
known only for free electrons or for their motion in a pure Coulomb field.
Therefore, in order to facilitate the use of Green's functions also for atoms
and ions other than the hydrogen--like ions, here we provide an extension to
the Ratip program which supports the computation of relativistic
(one--electron) Green's functions in an -- arbitrarily given -- central--field
potential \rV(r). Different computational modes have been implemented to
define these effective potentials and to generate the radial Green's functions
for all bound--state energies . In addition, care has been taken to
provide a user--friendly component of the Ratip package by utilizing features
of the Fortran 90/95 standard such as data structures, allocatable arrays, or a
module--oriented design.Comment: 20 pages, 1 figur
Correlated EoM and Distributions for A=6 Nuclei
Energy spectra and electromagnetic transitions of nuclei are strongly
depending from the correlations of the bound nucleons. Two particle
correlations are responsible for the scattering of model particles either to
low momentum- or to high momentum-states. The low momentum states form the
model space while the high momentum states are used to calculate the G-matrix.
The three and higher order particle correlations do not play a role in the
latter calculation especially if the correlations induced by the scattering
operator are of sufficient short range. They modify however, via the long tail
of the nuclear potential, the Slater determinant of the A particles by
generating excited Slater's determinants. In this work the influence of the
correlations on the level structure and ground state distributions of even open
shell nuclei is analyzed via the boson dynamic correlation model BDCM. The
model is based on the unitary operator ({\it S} is the correlation
operator) formalism which in this paper is presented within a non perturbative
approximation. The low lying spectrum calculated for Li reproduce very well
the experimental spectrum while for He a charge radius slightly larger than
that obtained within the isotopic-shift (IS) theory has been calculated. Good
agreement between theoretical and experimental results has been obtained
without the introduction of a genuine three body force.Comment: 25 pages 4 figures. To be published in the Progress Theoretical
Physic
Compton scattering of twisted light: angular distribution and polarization of scattered photons
Compton scattering of twisted photons is investigated within a
non-relativistic framework using first-order perturbation theory. We formulate
the problem in the density matrix theory, which enables one to gain new
insights into scattering processes of twisted particles by exploiting the
symmetries of the system. In particular, we analyze how the angular
distribution and polarization of the scattered photons are affected by the
parameters of the initial beam such as the opening angle and the projection of
orbital angular momentum. We present analytical and numerical results for the
angular distribution and the polarization of Compton scattered photons for
initially twisted light and compare them with the standard case of plane-wave
light
Extended Cluster Model for Light, and Medium Nuclei
The structures, the electromagnetic transitions, and the beta decay strengths
of exotic nuclei are investigated within an extended cluster model. We start by
deriving an effective nuclear Hamiltonian within the correlation
operator. Tensor forces are introduced in a perturbative expansion which
includes up to the second order terms. Within this Hamiltonian we calculate the
distributions and the radii of A=3,~4 nuclei. For exotic nuclei characterized
by n valence protons/neutrons we excite the structure of the closed shell
nuclei via mixed modes formed by considering correlations operators of higher
order. Good results have been obtained for the calculated transitions and for
the beta decay transition probabilities.Comment: 8-pages, 5-figure
Multipartite W states for chains of atoms conveyed through an optical cavity
We propose and work out a scheme to generate the entangled W states for a
chain of N four-level atoms which are transported through an optical cavity by
means of an optical lattice. This scheme is based on the combined laser-cavity
mediated interaction between distant and equally separated atoms and works in a
completely deterministic way for qubits encoded by two hyperfine levels of the
atoms. Only two parameters, namely the distance between the atoms and the
velocity of the chain, determine the effective interaction among the atoms and,
therefore, the degree of entanglement that is obtained for the overall chain of
N qubits. In particular, we work out the parameter regions for which the W
states are generated most reliably for chains of N = 2,3,4 and 5 atoms. In
addition, we analyze the sensitivity in the formation of entanglement for such
chains of qubits due to uncertainties produced by the oscillations of atoms in
optical lattices.Comment: 12 pages, revised version accepted in PR
Monte-Carlo approach to calculate the proton stopping in warm dense matter within particle-in-cell simulations
A Monte-Carlo approach to proton stopping in warm dense matter is implemented
into an existing particle-in-cell code. The model is based on multiple
binary-collisions among electron-electron, electron-ion and ion-ion, taking
into account contributions from both free and bound electrons, and allows to
calculate particle stopping in much more natural manner. At low temperature
limit, when ``all'' electron are bounded at the nucleus, the stopping power
converges to the predictions of Bethe-Bloch theory, which shows good
consistency with data provided by the NIST. With the rising of temperatures,
more and more bound electron are ionized, thus giving rise to an increased
stopping power to cold matter, which is consistent with the report of a
recently experimental measurement [Phys. Rev. Lett. 114, 215002 (2015)]. When
temperature is further increased, with ionizations reaching the maximum,
lowered stopping power is observed, which is due to the suppression of
collision frequency between projected proton beam and hot plasmas in the
target.Comment: 6 pages, 4 figure
Monte-Carlo approach to calculate the ionization of warm dense matter within particle-in-cell simulations
A physical model based on a Monte-Carlo approach is proposed to calculate the
ionization dynam- ics of warm dense matters (WDM) within particle-in-cell
simulations, and where the impact (col- lision) ionization (CI), electron-ion
recombination (RE) and ionization potential depression (IPD) by surrounding
plasmas are taken into consideration self-consistently. When compared with
other models, which are applied in the literature for plasmas near thermal
equilibrium, the temporal re- laxation of ionization dynamics can also be
simulated by the proposed model. Besides, this model is general and can be
applied for both single elements and alloys with quite different composi-
tions. The proposed model is implemented into a particle-in-cell (PIC) code,
with (final) ionization equilibriums sustained by competitions between CI and
its inverse process (i.e., RE). Comparisons between the full model and model
without IPD or RE are performed. Our results indicate that for bulk aluminium
in the WDM regime, i) the averaged ionization degree increases by including
IPD; while ii) the averaged ionization degree is significantly over estimated
when the RE is neglected. A direct comparison from the PIC code is made with
the existing models for the dependence of averaged ionization degree on thermal
equilibrium temperatures, and shows good agreements with that generated from
Saha-Boltzmann model or/and FLYCHK code.Comment: 7 pages, 4 figure
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