59 research outputs found
Solution of the Skyrme HF+BCS equation on a 3D mesh. II. A new version of the Ev8 code
We describe a new version of the EV8 code that solves the nuclear
Skyrme-Hartree-Fock+BCS problem using a 3-dimensional cartesian mesh. Several
new features have been implemented with respect to the earlier version
published in 2005. In particular, the numerical accuracy has been improved for
a given mesh size by (i) implementing a new solver to determine the Coulomb
potential for protons (ii) implementing a more precise method to calculate the
derivatives on a mesh that had already been implemented earlier in our
beyond-mean-field codes. The code has been made very flexible to enable the use
of a large variety of Skyrme energy density functionals that have been
introduced in the last years. Finally, the treatment of the constraints that
can be introduced in the mean-field equations has been improved. The code Ev8
is today the tool of choice to study the variation of the energy of a nucleus
from its ground state to very elongated or triaxial deformations with a
well-controlled accuracy.Comment: 24 pages, 3 figure
Finite-temperature mean-field approximations for shell model Hamiltonians: the code HF-SHELL
We present the code HF-SHELL for solving the self-consistent mean-field
equations for configuration-interaction shell model Hamiltonians in the
proton-neutron formalism. The code can calculate both ground-state and
finite-temperature properties in the Hartree-Fock (HF),
HF+Bardeen-Cooper-Schrieffer (HF+BCS), and the Hartree-Fock-Bogoliubov (HFB)
mean-field approximations. Particle-number projection after variation is
incorporated to reduce the grand-canonical ensemble to the canonical ensemble,
making the code particularly suitable for the calculation of nuclear state
densities. The code does not impose axial symmetry and allows for triaxial
quadrupole deformations. The self-consistency cycle is particularly robust
through the use of the heavy-ball optimization technique and the implementation
of different options to constrain the quadrupole degrees of freedom.Comment: 18 pages, 5 figures, source code repository can be found at
http://github.com/wryssens/hf-shel
Skyrme-Hartree-Fock-Bogoliubov mass models on a 3D mesh: II. Time-reversal symmetry breaking
Models based on nuclear energy density functionals can provide access to a
multitude of observables for thousands of nuclei in a single framework with
microscopic foundations. Such models can rival the accuracy of more
phenomenological approaches, but doing so requires adjusting parameters to
thousands of nuclear masses. To keep such large-scale fits feasible, several
symmetry restrictions are generally imposed on the nuclear configurations. One
such example is time-reversal invariance, which is generally enforced via the
Equal Filling Approximation (EFA). Here we lift this assumption, enabling us to
access the spin and current densities in the ground states of odd-mass and
odd-odd nuclei and which contribute to the total energy of such nuclei through
so-called "time-odd" terms. We present here the Skyrme-based BSkG2 model whose
parameters were adjusted to essentially all known nuclear masses without
relying on the EFA, refining our earlier work [G. Scamps et al., EPJA 57, 333
(2021), arXiv:2011.07904]. Moving beyond ground state properties, we also
incorporated information on the fission barriers of actinide nuclei in the
parameter adjustment. The resulting model achieves a root-mean-square (rms)
deviation of (i) 0.678 MeV on 2457 known masses, (ii) 0.027 fm on 884 measured
charge radii, (iii) 0.44 MeV and 0.47 MeV, respectively, on 45 reference values
for primary and secondary fission barriers of actinide nuclei, and (iv) 0.49
MeV on 28 fission isomer excitation energies. We limit ourselves here to a
description of the model and the study the impact of lifting the EFA on ground
state properties such as binding energies, deformation and pairing, deferring a
detailed discussion of fission to a forthcoming paper.Comment: 30 pages, 15 figure
Skyrme-Hartree-Fock-Bogoliubov mass models on a 3D mesh: III. From atomic nuclei to neutron stars
We present BSkG3, the latest entry in the Brussels-Skyrme-on-a-grid series of
large-scale models of nuclear structure based on an energy density functional.
Compared to its predecessors, the new model offers a more realistic description
of nucleonic matter at the extreme densities relevant to neutron stars. We
achieve the former by incorporating a constraint on the infinite nuclear matter
properties at high densities in the parameter adjustment, ensuring in this way
that the predictions of BSkG3 for the nuclear Equation of State are compatible
with the observational evidence for heavy pulsars with .
Instead of the usual phenomenological pairing terms, we also employ a more
microscopically founded treatment of nucleon pairing, resulting in
extrapolations to high densities that are in line with the predictions of
advanced many-body methods and are hence more suited to the study of
superfluidity in neutron stars. By adopting an extended form of the Skyrme
functional, we are able to reconcile the description of matter at high
densities and at saturation density: the new model further refines the
description of atomic nuclei offered by its predecessors. A qualitative
improvement is our inclusion of ground state reflection asymmetry, in addition
to the spontaneous breaking of rotational, axial, and time-reversal symmetry.
Quantitatively, the model offers lowered root-mean-square deviations on 2457
masses (0.631 MeV), 810 charge radii (0.0237 fm) and an unmatched accuracy with
respect to 45 primary fission barriers of actinide nuclei (0.33 MeV).
Reconciling the complexity of neutron stars with those of atomic nuclei
establishes BSkG3 as a tool of choice for applications to nuclear structure,
the nuclear equation of state and nuclear astrophysics in general
Progress on Brussels-Skyrme atomic mass models on a grid: stiff neutron matter equation of state
We report here the current developments on the Brussels-Skyrme-on-a-Grid
(BSkG) atomic mass models. In comparison with our previous models, BSkG3
improves the infinite nuclear matter (INM) properties which opens its
applications to neutron stars. The results presented here show that BSkG3
preserve the excellent agreement with experimental nuclear masses and radii,
together with fission barriers of actinides obtained by BSkG1 and BSkG2, while
the nuclear matter properties are considerably improved.Comment: 3 pages, 2 figure
The mass of odd-odd nuclei in microscopic mass models
Accurate estimates of the binding energy of nuclei far from stability that
cannot be produced in the laboratory are crucial to our understanding of
nuclear processes in astrophysical scenarios. Models based on energy density
functionals have shown that they are capable of reproducing all known masses
with root-mean-square error better than 800 keV, while retaining a firm
microscopic foundation. However, it was recently pointed out in [M. Hukkanen et
al., arXiv:2210.10674] that the recent BSkG1 model fails to account for a
contribution to the binding energy that is specific to odd-odd nuclei, and
which can be studied by using appropriate mass difference formulas. We analyse
here the (lacking) performance of three recent microscopic mass models with
respect to such formulas and examine possibilities to remedy this deficiency in
the future.Comment: 6 pages, 2 figures; Contribution to the proceedings of INPC 2022,
Cape Town, South Afric
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