arXiv subjects

P. -G. Reinhard

Publications and source records attributed to P. -G. Reinhard.

At least 127 records · Page 7Linked to original sources

arXiv2010

Properties of odd nuclei and the impact of time-odd mean fields: A systematic Skyrme-Hartree-Fock analysis

We present a systematic analysis of the description of odd nuclei by the Skyrme-Hartree-Fock approach augmented with pairing in BCS approximation and blocking of the odd nucleon. Current and spin densities in the Skyrme functional produce time-odd mean fields (TOMF) for odd nuclei. Their effect on basic properties (binding energies, odd-even staggering, separation energies and spectra) is investigated for the three Skyrme parameterizations SkI3, SLy6, and SV-bas. About 1300 spherical and axially-deformed odd nuclei with 16 < Z < 92 are considered. The calculations demonstrate that the TOMF effect is generally small, although not fully negligible. The influence of the Skyrme parameterization and the consistency of the calculations are much more important. With a proper choice of the parameterization, a good description of binding energies and their differences is obtained, comparable to that for even nuclei. The description of low-energy excitation spectra of odd nuclei is of varying quality depending on the nucleus.

nucl-th↗

arXiv2010

Microscopic study of the $^{132,124}$Sn+$^{96}$Zr reactions: dynamic excitation energy, energy-dependent heavy-ion potential, and capture cross section

We study reactions between neutron-rich $^{132}$Sn nucleus and $^{96}$Zr within a dynamic microscopic theory at energies in the vicinity of the ion-ion potential barrier peak, and we compare the properties to those of the stable system $^{124}$Sn+$^{96}$Zr. The calculations are carried out on a three-dimensional lattice using the density-constrained Time-Dependent Hartree-Fock method. In particular, we calculate the dynamic excitation energy $E^*(t)$ and the quadrupole moment of the dinuclear system, $Q_{20}(t)$, during the initial stages of the heavy-ion collision. Capture cross sections for the two reactions are analyzed in terms of dynamic effects and a comparison with recently measured data is given.

nucl-th↗

arXiv2010

The Generalized SIC-OEP formalism and the Generalized SIC-Slater approximation (stationary and time-dependent cases)

We present a generalized formulation of the Optimized Effective Potential (OEP) approach to the Self Interaction Correction (SIC) problem in Time Dependent (TD) Density Functional Theory (DFT). The formulation relies on the introduction of a double set of single electron orbitals. It allows the derivation of a generalized Slater approximation to the full OEP formulation, which extends the domain of validity of the standard Slater approximation. We discuss both formal aspects and practical applications of the new formalism and give illustrations in cluster and molecules. The new formalism provides a valuable ansatz to more elaborate (and computationally very demanding) full TD OEP and full TD SIC calculations especially in the linear domain.

quant-ph↗

arXiv2010

The information content of a new observable: the case of the nuclear neutron skin

We address two questions pertaining to the uniqueness and usefulness of a new observable: (i) Considering the current theoretical knowledge, what novel information does new measurement bring in? (ii) How can new data reduce uncertainties of current theoretical models? We illustrate these points by studying the radius of the neutron distribution of a heavy nucleus, a quantity related to the equation of state for neutron matter that determines properties of nuclei and neutron stars. By systematically varying parameters of two theoretical models and studying the resulting confidence ellipsoid, we quantify the relationships between the neutron skin and various properties of finite nuclei and infinite nuclear matter. Using the covariance analysis, we identify observables and pseudo-observables that correlate, and do not correlate, with the neutron skin. By adding the information on the neutron radius to the pool of observables determining the energy functional, we show how precise experimental determination of the neutron radius in $^{208}$Pb would reduce theoretical uncertainties on the neutron matter equation of state.

nucl-th↗

arXiv2010

Entrance Channel Dynamics of Hot and Cold Fusion Reactions Leading to Superheavy Elements

We investigate the entrance channel dynamics for the reactions $\mathrm{^{70}Zn}+\mathrm{^{208}Pb}$ and $\mathrm{^{48}Ca}+\mathrm{^{238}U}$ using the fully microscopic time-dependent Hartree-Fock (TDHF) theory coupled with a density constraint. We calculate excitation energies and capture cross-sections relevant for the study of superheavy formations. We discuss the deformation dependence of the ion-ion potential for the $\mathrm{^{48}Ca}+\mathrm{^{238}U}$ system and perform an alignment angle averaging for the calculation of the capture cross-section. The results show that this parameter-free approach can generate results in good agreement with experiment and other theories.

nucl-th↗

arXiv2010

Microscopic Description of Nuclear Fission Dynamics

We discuss possible avenues to study fission dynamics starting from a time-dependent mean-field approach. Previous attempts to study fission dynamics using the time-dependent Hartree-Fock (TDHF) theory are analyzed. We argue that different initial conditions may be needed to describe fission dynamics depending on the specifics of the fission phenomenon and propose various approaches towards this goal. In particular, we provide preliminary calculations for studying fission following a heavy-ion reaction using TDHF with a density contraint. Regarding prompt muon-induced fission, we also suggest a new approach for combining the time-evolution of the muonic wave function with a microscopic treatment of fission dynamics via TDHF.

nucl-th↗

arXiv2010

Non-adiabatic effects in the irradiation of ethylene

In the framework of the time dependent local density approximation, applied to valence electrons, coupled non-adiabatically to molecular dynamics of ions, the irradiations of ethylene by laser and fast charged projectiles are studied. We find that the Coulomb fragmentation sensitively depends on the laser frequency and on the charge of the projectile.

cond-mat.other↗

arXiv2010

Exploration of dynamical regimes of irradiated small protonated water clusters

We explore from a theoretical perspective the dynamical response of small water clusters, (H$_2$O)$_n$H$_3$O$^+$ with $n=1,2,3$, to a short laser pulse for various frequencies, from infrared (IR) to ultra-violet (UV) and intensities (from $6\times10^{13}$ W/cm$^2$ to $5\times10^{14}$ W/cm$^2$). To that end, we use time-dependent local-density approximation for the electrons, coupled to molecular dynamics for the atomic cores (TDLDA-MD). The local-density approximation is augmented by a self-interaction correction (SIC) to allow for a correct description of electron emission. For IR frequencies, we see a direct coupling of the laser field to the very light H$^+$ ions in the clusters. Resonant coupling (in the UV) and/or higher intensities lead to fast ionization with subsequent Coulomb explosion. The stability against Coulomb pressure increases with system size. Excitation to lower ionization stages induced strong ionic vibrations. These maintain rather harmonic pattern in spite of the sizeable amplitudes (often 10% of the bond length).

cond-mat.other↗

arXiv2010

Fission of super-heavy nuclei explored with Skyrme forces

We present a large scale survey of life-times for spontaneous fission in the regime of super-heavy elements (SHE), i.e. nuclei with Z=104-122. This is done on the basis of the Skyrme-Hartree-Fock model. The axially symmetric fission path is computed using a quadrupole constraint. Self-consistent cranking is used for the collective masses and associated quantum corrections. The actual tunneling probability is estimated by the WKB approximation. Three typical Skyrme forces are used to explore the sensitivity of the results. Benchmarks in the regime Z=104-108 show an acceptable agreement. The general systematics reflects nicely the islands of shell stabilization and the crossover from $α$-decay to fission for the decay chains from the region of Z/N=118/176.

nucl-th↗

arXiv2010

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.

nucl-th↗

arXiv2010

Spin-flip M1 giant resonance as a challenge for Skyrme forces

Despite a great success of the Skyrme mean-field approach in exploration of nuclear dynamics, it seems to fail in description of the spin-flip M1 giant resonance. The results for different Skyrme parameterizations are contradictory and poorly agree with experiment. In particular, there is no parameterization which simultaneously describes the one-peak gross structure of M1 strength in doubly magic nuclei and two-peak structure in heavy deformed nuclei. The reason of this mismatch could lie in an unsatisfactory treatment of spin correlations and spin-orbit interaction. We discuss the present status of the problem and possible ways of its solution. In particular, we inspect i) the interplay of the collective shift and spin-orbit splitting, ii) the isovector M1 response versus isospin-mixed responses, and iii) the role of tensor and isovector spin-orbit interaction.

nucl-th↗

arXiv2010

Angular distributions of electrons emitted from free and deposited Na$_8$ clusters

We explore from a theoretical perspective angular distributions of electrons emitted from a Na$_8$ cluster after excitation by a short laser pulse. The tool of the study is time-dependent density-functional theory (TDDFT) at the level of the local-density approximation (LDA) augmented by a self-interaction correction (SIC) to put emission properties in order. We consider free Na$_8$ and Na$_8$ deposited on the surfaces MgO(001) or Ar(001). For the case of free Na$_8$, we distinguish between a hypothetical situation of known cluster orientation and a more realistic ensemble of orientations. We also consider the angular distributions for emission from separate single-electron levels.

cond-mat.other↗

arXiv2010

Deposition of Na Clusters on MgO(001)

We investigate the dynamics of deposition of small Na clusters on MgO(001) surface. A hierarchical modeling is used combining Quantum Mechanical with Molecular Mechanical (QM/MM) description. Full time-dependent density-functional theory is used for the cluster electrons while the substrate atoms are treated at a classical level. We consider Na$_6$ and Na$_8$ at various impact energies. We analyze the dependence on cluster geometry, trends with impact energy, and energy balance. We compare the results with deposit on the much softer Ar(001) surface.

cond-mat.other↗

arXiv2009

Laser-driven nonlinear cluster dynamics

Laser excitation of nanometer-sized atomic and molecular clusters offers various opportunities to explore and control ultrafast many-particle dynamics. Whereas weak laser fields allow the analysis of photoionization, excited-state relaxation, and structural modifications on these finite quantum systems, large-amplitude collective electron motion and Coulomb explosion can be induced with intense laser pulses. This review provides an overview of key phenomena arising from laser-cluster interactions with focus on nonlinear optical excitations and discusses the underlying processes according to the current understanding. A brief general survey covers basic cluster properties and excitation mechanisms relevant for laser-driven cluster dynamics. Then, after an excursion in theoretical and experimental methods, results for single- and multiphoton excitations are reviewed with emphasis on signatures from time- and angular resolved photoemission. A key issue of this review is the broad spectrum of phenomena arising from clusters exposed to strong fields, where the interaction with the laser pulse creates short-lived and dense nanoplasmas. The implications for technical developments include the controlled generation of ion, electron, and radiation pulses, as will be addressed along with corresponding examples. Finally, future prospects of laser-cluster research as well as experimental and theoretical challenges are discussed.

physics.atm-clus↗

arXiv2009

Skyrme-Random-Phase-Approximation description of spin-flip and orbital giant resonances

The self-consistent separable random-phase approximation (SRPA) model with Skyrme forces is extended to the case of magnetic excitations and applied to the description of spin-flip and orbital M1 giant resonances in the isotopic chain $^{142-152}$Nd. The Skyrme forces SkT6, SkM*, SLy6 and SkI3 are used. The calculations show the onset of the scissors mode with increasing deformation. A specific three-peak structure of the spin-flip response is found and explained by particular neutron and proton spin-flip transitions. Although the employed forces provide an acceptable qualitative description, the Skyrme functional still needs further improvement to reproduce quantitatively the experimental data.

nucl-th↗

arXiv2009

Time-dependent Generalized SIC-OEP formalism and Generalized SIC-Slater approximation

We propose a simplification of the full "2 sets" Time dependent Self Interaction Correction (TD-SIC) method, applying the Optimized Effective Potential (OEP) method. The new resulting scheme is called time-dependent "Generalized SIC-OEP". A straightforward approximation, using the spatial localization of one set of orbitals, leads to the "Generalized SIC-Slater" formalism. We show that it represents a great improvement compared to the traditional SIC-Slater/KLI formalisms.

quant-ph↗

arXiv2009

Microscopic Calculation of Pre-Compound Excitation Energies for Heavy-Ion Collisions

We introduce a microscopic approach for calculating the excitation energies of systems formed during heavy-ion collisions. The method is based on time-dependent Hartree-Fock (TDHF) theory and allows the study of the excitation energy as a function of time or ion-ion separation distance. We discuss how this excitation energy is related to the estimate of the excitation energy using the reaction $Q$-value, as well as its implications for dinuclear pre-compound systems formed during heavy-ion collisions.

nucl-th↗

arXiv2009

Polarizibilities as a test of localized approximations to the self-interaction correction

We present applications of the recently introduced ``Generalized SIC-Slater'' scheme which provides a simple Self-Interaction Correction approximation in the framework of the Optimized Effective Potential. We focus on the computation of static polarizabilities which are known to constitute stringent tests for Density Functional Theory. We apply the new method to model H chains, but also to more realistic systems such as C4 (organic) chains, and less symmetrical systems such as a Na5 (metallic) cluster. Comparison is made with other SIC schemes, especially with the standard SIC-Slater one.

quant-ph↗