3,906 research outputs found
Self-consistent Skyrme QRPA for use in axially-symmetric nuclei of arbitrary mass
We describe a new implementation of the quasiparticle random phase
approximation (QRPA) in axially-symmetric deformed nuclei with Skyrme and
volume-pairing energy-density functionals. After using a variety of tests to
demonstrate the accuracy of the code in ^{24,26}Mg and ^{16}O, we report the
first fully self-consistent application of the Skyrme QRPA to a heavy deformed
nucleus, calculating strength distributions for several K^pi in ^{172}Yb. We
present energy-weighted sums, properties of gamma-vibrational and low-energy
K^pi=0^+ states, and the complete isovector E1 strength function. The QRPA
calculation reproduces the properties of the low-lying 2^+ states as well or
better than it typically does in spherical nuclei.Comment: 5 pages, 6 figure
Testing He density distributions by calculations of total reaction cross-sections of He+Si
Calculations of the He + Si total reaction cross sections at
intermediate energies are performed on the basis of the Glauber-Sitenko
microscopic optical-limit model. The target-nucleus density distribution is
taken from the electron-nucleus scattering data, and the He densities
are used as they are derived in different models. The results of the
calculations are compared with the existing experimental data. The effects of
the density tails of the projectile nuclei as well as the role of shell
admixtures and short-range correlations are analyzed.Comment: 10 pages, 5 figures. Submitted to the International Journal of Modern
Physics
Density functional theory and Kohn-Sham scheme for self-bound systems
We demonstrate how the separation of the total energy of a self-bound system
into a functional of the internal one-body Fermionic density and a function of
an arbitrary wave vector describing the center-of-mass kinetic energy can be
used to set-up an "internal" Kohn-Sham scheme.Comment: 6 pages. To be published in Phys. Rev.
Configuration Mixing within the Energy Density Functional Formalism: Removing Spurious Contributions from Non-Diagonal Energy Kernels
Multi-reference calculations along the lines of the Generator Coordinate
Method or the restoration of broken symmetries within the nuclear Energy
Density Functional (EDF) framework are becoming a standard tool in nuclear
structure physics. These calculations rely on the extension of a
single-reference energy functional, of the Gogny or the Skyrme types, to
non-diagonal energy kernels. There is no rigorous constructive framework for
this extension so far. The commonly accepted way proceeds by formal analogy
with the expressions obtained when applying the generalized Wick theorem to the
non-diagonal matrix element of a Hamilton operator between two product states.
It is pointed out that this procedure is ill-defined when extended to EDF
calculations as the generalized Wick theorem is taken outside of its range of
applicability. In particular, such a procedure is responsible for the
appearance of spurious divergences and steps in multi-reference EDF energies,
as was recently observed in calculations restoring particle number or angular
momentum. In the present work, we give a formal analysis of the origin of this
problem for calculations with and without pairing, i.e. constructing the
density matrices from either Slater determinants or quasi-particle vacua. We
propose a correction to energy kernels that removes the divergences and steps,
and which is applicable to calculations based on any symmetry restoration or
generator coordinate. The method is formally illustrated for particle number
restoration and is specified to configuration mixing calculations based on
Slater determinants.Comment: 27 pages, 1 figure, accepted for publication in PR
Exploring continuum structures with a pseudo-state basis
The ability of a recently developed square-integrable discrete basis to
represent the properties of the continuum of a two-body system is investigated.
The basis is obtained performing a simple analytic local scale transformation
to the harmonic oscillator basis. Scattering phase-shifts and the electric
transition probabilities B(E1) and B(E2) have been evaluated for several
potentials using the proposed basis. Both quantities are found to be in
excellent agreement with the exact values calculated from the true scattering
states. The basis has been applied to describe the projectile continuum in the
6He scattering by 12C and 208Pb targets at 240 MeV/nucleon and the 11Be
scattering by 12C at 67 MeV/nucleon. The calculated breakup differential cross
sections are found to be in very good agreement with the available experimental
data for these reactions.Comment: 17 pages, 10 figures (Version to appear in Phys. Rev. C
Local structure study of In_xGa_(1-x)As semiconductor alloys using High Energy Synchrotron X-ray Diffraction
Nearest and higher neighbor distances as well as bond length distributions
(static and thermal) of the In_xGa_(1-x)As (0<x<1) semiconductor alloys have
been obtained from high real-space resolution atomic pair distribution
functions (PDFs). Using this structural information, we modeled the local
atomic displacements in In_xGa_(1-x)As alloys. From a supercell model based on
the Kirkwood potential, we obtained 3-D As and (In,Ga) ensemble averaged
probability distributions. This clearly shows that As atom displacements are
highly directional and can be represented as a combination of and
displacements. Examination of the Kirkwood model indicates that the standard
deviation (sigma) of the static disorder on the (In,Ga) sublattice is around
60% of the value on the As sublattice and the (In,Ga) atomic displacements are
much more isotropic than those on the As sublattice. The single crystal diffuse
scattering calculated from the Kirkwood model shows that atomic displacements
are most strongly correlated along directions.Comment: 10 pages, 12 figure
Quadrupole deformations of neutron-drip-line nuclei studied within the Skyrme Hartree-Fock-Bogolyubov approach
We introduce a local-scaling point transformation to allow for modifying the
asymptotic properties of the deformed three-dimensional Cartesian harmonic
oscillator wave functions. The resulting single-particle bases are very well
suited for solving the Hartree-Fock-Bogoliubov equations for deformed drip-line
nuclei. We then present results of self-consistent calculations performed for
the Mg isotopes and for light nuclei located near the two-neutron drip line.
The results suggest that for all even-even elements with =10--18 the most
weakly-bound nucleus has an oblate ground-state shape.Comment: 20 pages, 7 figure
Ab initio derivation of model energy density functionals
I propose a simple and manageable method that allows for deriving coupling constants of model energy density functionals (EDFs) directly from ab initio calculations performed for finite fermion systems. A proof-of-principle application allows for linking properties of finite nuclei, determined by using the nuclear nonlocal Gogny functional, to the coupling constants of the quasilocal Skyrme functional. The method does not rely on properties of infinite fermion systems but on the ab initio calculations in finite systems. It also allows for quantifying merits of different model EDFs in describing the ab initio results
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