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E. Suraud

Publications and source records attributed to E. Suraud.

47 records · Page 3Linked to original sources
arXiv2007

Structural properties and optical response of Na clusters in Ne, Ar, and Kr matrices

We discuss the structural properties and optical response of a small Na cluster inside rare gas (RG) matrices of Ne, Ar, or Kr atoms. The mixed systems are described with a hierarchical model, treating the cluster at a quantum mechanical level and the matrix atoms classically in terms of their positions and polarizations. We pay special attention to the differences caused by the different matrix types. These differences can be explained by the interplay of core repulsion and dipole attraction in the interaction between the cluster electrons and the RG atoms.

cond-mat.other↗
arXiv2007

Size and charge effects on the deposition of Na on Ar

We discuss the dynamical deposition of the Na atom, the Na$^+$ in and the Na$_6$ cluster on finite Ar clusters mocking up an infinite Ar surface. We analyze this scenario as a function of projectile initial kinetic energy and of the size the target cluster.

cond-mat.other↗
arXiv2007

Dynamics of metal clusters in rare gas clusters

We investigate the dynamics of Na clusters embedded in Ar matrices. We use a hierarchical approach, accounting microscopically for the cluster's degrees of freedom and more coarsely for the matrix. The dynamical polarizability of the Ar atoms and the strong Pauli-repulsion exerted by the Ar-electrons are taken into account. We discuss the impact of the matrix on the cluster gross properties and on its optical response. We then consider a realistic case of irradiation by a moderately intense laser and discuss the impact of the matrix on the hindrance of the explosion, as well as a possible pump probe scenario for analyzing dynamical responses.

cond-mat.other↗
arXiv2007

Systematics of spin-polarized small Na clusters

Inspired by recent experiments on fully spin polarized Na clusters, we perform a systematic survey of neutral Na clusters at all conceivable spin polarizations. We study the impact of spin state on ionic configuration, on global shape, and on optical response. For small clusters, the magic electronic shell at 4 spin-up electrons is a dominating feature leading to preferred binding for all clusters having four spin-up electrons (combined with 1 to 4 spin-down electrons). Such a preference fades away for larger systems where the unpolarized state is generally preferred.

physics.atm-clus↗
arXiv2006

Exploration of electronic quadrupole states in atomic clusters by two-photon processes

We analyze particular two-photon processes as possible means to explore electronic quadrupole states in free small deformed atomic clusters. The analysis is done in the time-dependent local density approximation (TDLDA). It is shown that the direct two-photon population (DTP) and off-resonant stimulated Raman (ORSR) scattering can be effectively used for excitation of the quadrupole states in high-frequency (quadrupole plasmon) and low-frequency (infrared) regions, respectively. In ORSR, isolated dipole particle-hole states as well as the tail of the dipole plasmon can serve as an intermediate state. A simultaneous study of low- and high-frequency quadrupoles, combining DTP and ORSR, is most effective. Femtosecond pulses with intensities $I = 2\cdot 10^{10} - 2\cdot 10^{11} W/cm^2$ and pulse durations $T = 200 - 500$ fs are found to be optimal. Since the low-lying quadrupole states are dominated by one single electron-hole pair, their energies, being combined with the photoelectron data for hole states, allow to get the electron spectrum above the Fermi level and thus greatly extend our knowledge on the single particle spectra of clusters. Besides, the developed schemes allow to estimate the lifetime of the quadrupole states.

physics.atm-clus↗
arXiv2005

Modeling Na clusters in Ar matrices

We present a microscopic model for Na clusters embedded in raregas matrices. The valence electrons of the Na cluster are described by time-dependent density-functional theory at the level of the local-density approximation (LDA). Particular attention is paid to the semi-classical picture in terms of Vlasov-LDA. The Na ions and Argon atoms are handled as classical particles whereby the Ar atoms carry two degrees of freedom, position and dipole polarization. The interaction between Na ions and electrons is mediated through local pseudo-potentials. The coupling to the Ar atoms is described by (long-range) polarization potentials and (short-range) repulsive cores. The ingredients are taken from elsewhere developed standards. A final fine-tuning is performed using the NaAr molecule as benchmark. The model is then applied to embedded systems Na8ArN. By close comparison with quantum-mechanical results, we explore the capability of the Vlasov-LDA to describe such embedded clusters. We show that one can obtain a reasonable description by appropriate adjustments in the fine-tuning phase of the model.

physics.atm-clus↗
arXiv2004

Time resolved fission in metal clusters

We explore from a theoretical point of view pump and probe (P&P) analysis for fission of metal clusters where probe pulses are generalized to allow for scanning various frequencies. We show that it is possible to measure the time the system needs to develop to scission. This is achieved by a proper choice of both delay and frequency of the probe pulse. A more detailed analysis even allows to access the various intermediate stages of the fission process.

cond-mat.other↗
arXiv2002

Scissors modes in triaxial metal clusters

We study the scissors mode (orbital M1 excitations) in small Na clusters, triaxial metal clusters ${\rm Na}_{12}$ and ${\rm Na}_{16}$ and the close-to-spherical ${{\rm Na}_9}^+$, all described in DFT with detailed ionic background. The scissors modes built on spin-saturated ground and spin-polarized isomeric states are analyzed in virtue of both macroscopic collective and microscopic shell-model treatments. It is shown that the mutual destruction of Coulomb and the exchange-correlation parts of the residual interaction makes the collective shift small and the net effect can depend on details of the actual excited state. The crosstalk with dipole and spin-dipole modes is studied in detail. In particular, a strong crosstalk with spin-dipole negative-parity mode is found in the case of spin-polarized states. Triaxiality and ionic structure considerably complicate the scissors response, mainly at expense of stronger fragmentation of the strength. Nevertheless, even in these complicated cases the scissors mode is mainly determined by the global deformation. The detailed ionic structure destroys the spherical symmetry and can cause finite M1 response (transverse optical mode) even in clusters with zero global deformation. But its strength turns out to be much smaller than for the genuine scissors modes in deformed systems.

physics.atm-clus↗
arXiv1999

Beyond Mean Field Confrontation of Different Models with High Transverse Momentum Proton Spectra

Several models have been proposed to simulate heavy ion reactions beyond the mean field level. The lack of data in phase space regions which may be sensitive to different treatments of fluctuations made it difficult to judge these approaches. The recently published high energy proton spectra, measured in the reaction 94 AMeV Ar + Ta, allow for the first time for a comparison of the models with data. We find that these spectra are reproduced by Quantum Molecular Dynamics (QMD) and Boltzmann Uehling Uhlenbeck (BUU) calculations. Models like Boltzmann Langevin (BL) in which additional fluctuations in momentum space are introduced overpredict the proton yield at very high energies. The BL approach has been successfully used to describe the recently measured very subthreshold kaon production assuming that the fluctuations provide the necessary energy to overcome the threshold in two body collisions. Our new findings suggest that the very subthreshold kaon production cannot be due to two body scattering and thus remains a open problem.

nucl-th↗
arXiv1994

On the Formation of Transient (Na$_{19}$)$_2$ and (Na$_{20}$)$_2$ Cluster Dimers from Molecular Dynamics Simulations

By using tight binding molecular dynamics simulations, we discuss the possibilities to form (Na$_{19}$)$_2$ and (Na$_{20}$)$_2$ cluster dimers in sodium cluster collisions. In the case of Na$_{19}$ + Na$_{19}$, we show that the formation of a prolate dimer-like (Na$_{19}$)$_2$ maybe depend on the initial relative orientations of the colliding clusters. A similar study for Na$_{20}$ + Na$_{20}$ does not seem to show the same dependence on the initial orientations in the formation of the (Na$_{20}$)$_2$ cluster dimer.

cond-mat↗