Search results for "molecular dynamics"

Round Robin computer simulation of ejection probability in sputtering

1989

Abstract We have studied the ejection of a copper atom through a planar copper surface as a function of recoil velocity and depth of origin. Results were obtained from six molecular dynamics codes, four binary collision lattice simulation codes, and eight Monte Carlo codes. Most results were found with a Born-Mayer interaction potential between the atoms with Gibson 2 parameters and a planar surface barrier, but variations on this standard were allowed for, as well as differences in the adopted cutoff radius for the interaction potential, electronic stopping, and target temperature. Large differences were found between the predictions of the various codes, but the cause of these differences…

Mixture and dissolution of laser polarized noble gases: Spectroscopic and imaging applications

2012

Ordering effects in extreme high-resolution depth profiling with MeV ion beams

2012

Abstract The continuing development of depth profiling with MeV ion beam methods with depth resolutions in the nanometre, and even sub-nanometre, regime implies the resolved depth become comparable with the interatomic spacing. To investigate how short-range ordering influences depth profiles at these resolutions, we have employed a mathematical modelling approach. The radial, g ( r ) and depth distribution, g ( z ) functions were calculated for (1 0 0) surface, random and amorphous Si structures at 300 K produced using molecular dynamics simulations with the EDIP quasi-empirical potential. The results showed that short-range ordering lead to reduction of the scattering yield below the deep…

Crystallographic analysis of extended defects in diamond-type crystals

2005

Abstract To investigate irradiation-induced Si amorphization during its initial stages, we have performed a classical molecular-dynamics (MD) calculation for the case of self-irradiation by 5 keV ions at a low temperature of 100 K. We examined the geometry of self-interstitial atom (SIA) clusters using the pixel mapping (PM) method, on the output data of MD calculations. Perfect crystalline silicon (c-Si) is amorphized by self-irradiation, and we observe that many SIA are produced. During sequential self-irradiation, the most frequently observed species were isolated SIA, i.e. I1 (monomer). The fractions of SIA clusters decreased as I2 (dimer), I3 (trimer), and I4 (tetramer) clusters, respe…

A first estimate of $\eta/s$ in Au+Au reactions at E$_{\rm lab}=1.23$ $A$GeV

2020

The HADES experiment at GSI has recently provided data on the flow coefficients $v_1,...,v_4$ for protons in Au+Au reactions at $E_{\rm lab} = 1.23$~$A$GeV (or $\sqrt{s_\mathrm{NN}}=2.4$ GeV). This data allows to estimate the shear viscosity over entropy ratio, $\eta/s$ at low energies via a coarse graining analysis of the UrQMD transport simulations of the flow harmonics in comparison to the experimental data. By this we can provide for the first time an estimate of $\eta/s\approx0.65\pm0.15$ (or $(8\pm2)\,(4\pi)^{-1}$) at such low energies.

A predictive model for the electronic stopping force for molecular dynamic simulation (I)

2010

Abstract We have examined a predictive model for the electronic stopping force (dE/dx)e to be used in the classical molecular dynamic (MD) simulation. The essential term (dE/dx)proton of (dE/dx)e is based on the Lindhard–Winther theory, while the effective charge follows the Brandt–Kitagawa model. The (dE/dx)proton term is expressed by the electron local density ρ(r) defined by the Muffin-tin model and the Hartree–Fock–Slater approximation. This model had been proposed to explain the impact-parameter dependence of (dE/dx)e for channeling ions passing through a semiconductor. Here the energy dependence of the averaged 〈dE/dx〉e after thin-film transmission was examined, where the electron–pho…

Molecular dynamics simulation of the damage production in Al (110) surface with slow argon ions

1986

We have developed a molecular dynamics simulation program to gain more insight into the sputtering process, especially the damage produced by it. We have studied the sputtering of aluminium (110) surface with argon ions. The Morse pair potentail was used for Al−Al interaction, the Lennard-Jones potential for Ar−Ar interaction and both the Moliere potential and the universal potential of Ziegler et al. for Ar−Al interaction. An electronic friction term proportional to the particle velocities was also used. The studied incident argon ion energies and angles were 200 and 400 eV and 0° (normal), 25°, 45° and 75°, respectively. The calculated sputtering yield and the overall shape and the mean d…

Zero-field nuclear magnetic resonance spectroscopy of viscous liquids

2014

Abstract We report zero-field NMR measurements of a viscous organic liquid, ethylene glycol. Zero-field spectra were taken showing resolved scalar spin–spin coupling (J-coupling) for ethylene glycol at different temperatures and water contents. Molecular dynamics strongly affects the resonance linewidth, which closely follows viscosity. Quantum chemical calculations have been used to obtain the relative stability and coupling constants of all ethylene glycol conformers. The results show the potential of zero-field NMR as a probe of molecular structure and dynamics in a wide range of environments, including viscous fluids.

Insertion of Be Atoms inC60Fullerene Cages:Be@C60

1996

Radioactive endohedral {sup 7}Be@C{sub 60} can be detected using radiochemical and radiochromatographic techniques in the final solvent. Such a {sup 7}Be atom can penetrate into the C{sub 60} cage to produce {sup 7}Be@C{sub 60} by a recoil process of the nuclear reactions. An {ital ab} {ital initio} molecular dynamics simulation was carried out to demonstrate that a direct insertion process is really possible. Both the experimental and the theoretical results were consistent with each other. {copyright} {ital 1996 The American Physical Society.}

A dynamic load-balancing algorithm for molecular dynamics simulation on multi-processor systems

1991

Abstract A new algorithm for dynamic load-balancing on multi-processor systems and its application to the molecular dynamics simulation of the spinodal phase separation are presented. The load-balancer is distributed among the processors and embedded in the application itself. Tests performed on a transputer network show that the load-balancer behaves almost ideally in this application. The same approach can be easily extended to different multi-processor topologies or applications.