arXiv subjects

P. -G. Reinhard

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

At least 145 records · Page 8Linked to original sources

arXiv2009

Dynamics of clusters and molecules in contact with an environment

We present recent theoretical investigations on the dynamics of metal clusters in contact with an environment, deposited of embedded. This concerns soft deposition as well as irradiation of the deposited/embedded clusters by intense laser pulses. We discuss examples of applications for two typical test cases, Na clusters deposited on MgO(001) surface and Na clusters in/on Ar substrate. Both environments are insulators with sizeable polarizability. They differ in their geometrical and mechanical properties.

physics.atm-clus↗

arXiv2009

Skyrme-Rpa Description of Spin-Flip M1 Giant Resonance

The spin-flip M1 giant resonance is explored in the framework of Random Phase Approximation on the basis of the Skyrme energy functional. A representative set of eight Skyrme parameterizations (SkT6, SkM*, SLy6, SG2, SkO, SkO', SkI4, and SV-bas) is used. Light and heavy, spherical and deformed nuclei ($^{48}$Ca, $^{158}$Gd, $^{208}$Pb, and $^{238}$U) are considered. The calculations show that spin densities play a crucial role in forming the collective shift in the spectrum. The interplay of the collective shift and spin-orbit splitting determines the quality of the description. None of the considered Skyrme parameterizations is able to describe simultaneously the M1 strength distribution in closed-shell and open-shell nuclei. It is found that the problem lies in the relative positions of proton and neutron spin-orbit splitting. Necessity to involve the tensor and isovector spin-orbit interaction is called for.

nucl-th↗

arXiv2009

Criteria for nonlinear parameters of relativistic mean field models

Based on the properties of the critical and the actual effective masses of sigma and omega mesons, criteria to estimate the values of the isoscalar nonlinear terms of the standard relativistic mean field model that reproduce stable equations of state in respect to particle hole excitation at high densities are derived. The relation between nuclear matter stability and the symmetric nuclear matter properties are shown. The criteria are used to analyze in a more systematic way the high-density longitudinal and transverse instabilities of some parameter sets of relativistic mean field models. The critical role of the vector and vector-scalar nonlinear terms is also discussed quantitatively.

nucl-th↗

arXiv2009

Production of intense beams of mass-selected water cluster ions and theoretical study of atom-water interactions

The influences of water molecules surrounding biological molecules during irradiation with heavy particles (atoms,ions) are currently a major subject in radiation science on a molecular level. In order to elucidate the underlying complex reaction mechanisms we have initiated a joint experimental and theoretical investigation with the aim to make direct comparisons between experimental and theoretical results. As a first step, studies of collisions of a water molecule with a neutral projectile (C atom) at high velocities (> 0.1 a.u.), and with a charged projectile (proton) at low velocities (< 0.1 a.u.) have been studied within the microscopic framework. In particular, time-dependent density functional theory (TDDFT) was applied to the valence electrons and coupled non-adiabatically to Molecular dynamics (MD) for ionic cores. Complementary experimental developments have been carried out to study projectile interactions with accelerated (< 10 keV) and mass-selected cluster ions. The first size distributions of protonated water cluster ions H+(H_2O)_n (n=2-39) produced using this new apparatus are presented.

physics.atm-clus↗

arXiv2009

DFT studies of ethylene in femtosecond laser pulses

Using time-dependent density functional theory, applied to valence electrons, coupled non-adiabatically to molecular dynamics of the ions, we study the induced dynamics of ethylene subjected to the laser field. We demonstrate the reliable quality of such an approach in comparison to the experimental data on atomic and molecular properties. The impact of ionic motion on the ionization is discussed showing the importance of dealing with electronic and ionic degrees of freedom simultaneously. We explore the various excitation scenarios of ethylene as a function of the laser parameters. We find that the Coulomb fragmentation depends sensitively on the laser frequency. The high laser intensity can cause brute-force Coulomb explosion and the laser pulse length actually has influence on the excitation dynamics of ethylene.

physics.atm-clus↗

arXiv2009

High-order harmonic generation and multi-photon ionization of ethylene in laser fields

Applying time-dependent local density approximation (TDLDA), we study the high-order harmonic generation (HHG) of ethylene subjected to the one-color ($ω=2.72$ eV) and the two-color ($ω_1=2.72$ eV and $ω_2=5.44$ eV) ultrashort intense laser pulses. The HHG spectrum of ethylene in the one-color laser field shows the obvious plateaus and odd order harmonics are produced while the two-color laser field can result in the breaking of the symmetry and generation of the even order harmonic. The ionization probabilities are obtained showing the increase of the ionization probability of higher charge state by the two-color laser field. The temporal structures of HHG spectrum of ethylene is explored by means of the time-frequency analysis showing new insights of the HHG mechanisms in the one-color and the two-color laser fields.

physics.atm-clus↗

arXiv2009

Dipole excitations of Ar substrate in contact with Na clusters

e analyze the excitation of Ar substrate in contact with Na clusters using a previously developed hierarchical model for the description of the system constituted of a highly reactive metal cluster in contact with a rather inert substrate. Particular attention is paid to the dipole excitation of the Ar atoms and the energy stored therein. The Na clusters are considered at different charge states, anions, cations, and neutral clusters for the case of deposition and a highly ionized cluster embedded in a matrix. It is found that the dipole polarization of the Ar atoms stores the largest fraction of energy in the case of charged clusters. Some, although smaller, polarization is also observed for polar clusters, as Na$_6$. The effect is predominantly induced by the electrostatic interaction.

cond-mat.other↗

arXiv2008

Skyrme-Random-Phase-Approximation description of E1 strength in 92-100Mo

The isovector dipole E1 strength in Mo isotopes with A=92,94,96,98,100 is analyzed within the self-consistent separable random-phase approximation (SRPA) model with Skyrme forces SkT6, SkM*, SLy6, and SkI3. The special attention is paid to the low-energy region near the particle thresholds (4-12 MeV), which is important for understanding of astrophysical processes. We show that, due to a compensation effect, the influence of nuclear deformation on E1 strength below 10-12 MeV is quite modest. At the same time, in agreement with previous predictions, the deformation increases the strength at higher energy. At 4-8 MeV the strength is mainly determined by the tail of E1 giant resonance. The four Skyrme forces differ in description of the whole giant resonance but give rather similar results below 12 MeV.

nucl-th↗

arXiv2008

On the exact treatment of Time Dependent Self-Interaction Correction

We present a new formulation of the time-dependent self-interaction correction (TDSIC). It is derived variationally obeying explicitly the constraints on orthonormality of the occupied single-particle orbitals. The thus emerging rather involved symmetry condition amongst the orbitals is dealt with using two separate sets of (occupied) single-particle wavefunctions, related by a unitary transformation. The double-set TDSIC scheme is well suited for numerical implementation. We present results for laser-excited dynamics in a 1D model for a molecule and in fully fledged 3D calculations.

quant-ph↗

arXiv2008

Deposition dynamics of Na monomers and dimers on an Ar(001) substrate

We study deposition dynamics of Na and Na$_2$ on an Ar substrate, both species neutral as well as charged. The system is modeled by a hierarchical approach describing the Na valence electrons by time-dependent density-functional theory while Na core, Ar atoms and their dynamical polarizability are treated by molecular dynamics. We explore effects of Na charge and initial kinetic energy of the impinging Na system. We find that neutral Na is captured into a loosely bound adsorbate state for sufficiently low impact energy. The charged monomers are more efficiently captured and the cation Na$^+$ even penetrates the surface layer. For charged dimers, we come to different final configurations depending on the process, direct deposit of Na$_2^+$ as a whole, or sequential deposit. In any case, charge dramatically amplifies the excitation of the matrix, in particular at the side of the Ar dipoles. The presence of a charge also enhances the binding to the surface and favours accumulation of larger compounds.

cond-mat.mtrl-sci↗

arXiv2008

Improved Slater approximation to SIC-OEP

We propose a simplification of the Optimized Effective Potential (OEP) applied to the Self Interaction Correction (SIC) scheme of Density Functional Theory (DFT). The new scheme fulfills several key formal properties and turns out to be both simple and accurate. We show examples of applications on model molecules in terms of observables known to be especially sensitive to details of the SIC-OEP approach.

cond-mat.other↗

arXiv2008

Self-interaction correction in a simple model

We discuss various ways to handle self-interaction corrections (SIC) to Density Functional Theory (DFT) calculations. To that end, we use a simple model of few particles in a finite number of states together with a simple zero-range interaction for which full Hartree-Fock can easily be computed as a benchmark. The model allows to shed some light on the balance between orthonormality of the involved states and energy variance.

cond-mat.other↗

arXiv2008

Skyrme-Rpa Description of Dipole Giant Resonance in Heavy and Superheavy Nuclei

The E1(T=1) isovector dipole giant resonance (GDR) in heavy and super-heavy deformed nuclei is analyzed over a sample of 18 rare-earth nuclei, 4 actinides and three chains of super-heavy elements (Z=102, 114 and 120). Basis of the description is self-consistent separable RPA (SRPA) using the Skyrme force SLy6. The self-consistent model well reproduces the experimental data (energies and widths) in the rare-earth and actinide region. The trend of the resonance peak energies follows the estimates from collective models, showing a bias to the volume mode for the rare-earths isotopes and a mix of volume and surface modes for actinides and super-heavy elements. The widths of the GDR are mainly determined by the Landau fragmentation which in turn is found to be strongly influenced by deformation. A deformation splitting of the GDR can contribute about one third to the width and about 1 MeV further broadening can be associated to mechanism beyond the mean-field description (escape, coupling with complex configurations).

nucl-th↗

arXiv2008

Conservation Properties in the Time-Dependent Hartree Fock Theory

We discuss the conservation of angular momentum in nuclear time-dependent Hartree-Fock calculations for a numerical representation of wave functions and potentials on a three-dimensional cartesian grid. Free rotation of a deformed nucleus performs extremely well even for relatively coarse spatial grids. Heavy ion collisions produce a highly excited compound system associated with substantial nucleon emission. These emitted nucleons reach the bounds of the numerical box which leads to a decrease of angular momentum. We discuss strategies to distinguish the physically justified loss from numerical artifacts.

nucl-th↗

arXiv2008

Time-dependent density-functional theory with self-interaction correction

We discuss an extension of time-dependent density-functional theory by a self-interaction correction (SIC). A strictly variational formulation is given taking care of the necessary constraints. A manageable and transparent propagation scheme using two sets of wavefunctions is proposed and applied to laser excitation with subsequent ionization of a dimer molecule.

cond-mat.other↗

arXiv2007

TDDFT with Skyrme Forces: Effect of Time-Odd Densities on Electric Giant Resonances

Time-odd densities and their effect on electric giant resonances are investigated within the self-consistent separable random-phase-approximation (SRPA) model for various Skyrme forces (SkT6, SkO, SkM*, SIII, SGII, SLy4, SLy6, SkI3). Time-odd densities restore Galilean invariance of the Skyrme functional, violated by the effective-mass and spin-orbital terms. In even-even nuclei these densities do not contribute to the ground state but can affect the dynamics. As a particular case, we explore the role of the current density in description of isovector E1 and isoscalar E2 giant resonances in a chain of Nd spherical and deformed isotopes with A=134-158. Relation of the current to the effective masses and relevant parameters of the Skyrme functional is analyzed. It is shown that current contribution to E1 and E2 resonances is generally essential and fully determined by the values and signs of the isovector and isoscalar effective-mass parameters of the force. The contribution is the same for all the isotope chain, i.e. for both standard and exotic nuclei.

nucl-th↗

arXiv2007

Triaxiality and shape coexistence in Germanium isotopes

The ground-state deformations of the Ge isotopes are investigated in the framework of Gogny-Hartree-Fock-Bogoliubov (HFB) and Skyrme Hartree-Fock plus pairing in the BCS approximation. Five different Skyrme parametrizations are used to explore the influence of different effective masses and spin-orbit models. There is generally good agreement for binding energies and deformations (total quadrupole moment, triaxiality) with experimental data where available (i.e., in the valley of stability). All calculations agree in predicting a strong tendency for triaxial shapes in the Ge isotopes with only a few exceptions due to neutron (sub-)shell closures. The frequent occurrence of energetically very close shape isomers indicates that the underlying deformation energy landscape is very soft. The general triaxial softness of the Ge isotopes is demonstrated in the fully triaxial potential energy surface. The differences between the forces play an increasing role with increasing neutron number. This concerns particularly the influence of the spin-orbit model, which has a visible effect on the trend of binding energies towards the drip line. Different effective mass plays an important role in predicting the quadrupole and triaxial deformations. The pairing strength only weakly affects binding energies and total quadrupole deformations, but considerably influences triaxiality.

nucl-th↗

arXiv2007

Particle-Number Projection and the Density Functional Theory

In the framework of the Density Functional Theory for superconductors, we study the restoration of the particle number symmetry by means of the projection technique. Conceptual problems are outlined and numerical difficulties are discussed. Both are related to the fact that neither the many-body Hamiltonian nor the wave function of the system appear explicitly in the Density Functional Theory. Similar obstacles are encountered in self-consistent theories utilizing density-dependent effective interactions.

nucl-th↗