Domain-decomposition Parallelization for Molecular Dynamics Algorithm with Short-ranged Potentials on Epiphany Architecture

Many-core processor architecture is a promising paradigm for thedevelopment of modern supercomputers. In this paper, we consider theparallel implementation of the generic molecular dynamics algorithmfor the many-core Epiphany architecture. This architectureimplements a new type of many-core processor composed of 16 simplecores connected by a network on chip with mesh topology. Newapproaches to parallel programming are required to deploy thisprocessor. We use LAMMPS running on one 64-bit ARMv8 Cortex-A53 CPUcore for comparing the accuracy of the results of the presentedvariant of the molecular dynamics algorithm for Epiphany and itscomputational efficiency

HYDRATION STRUCTURE OF Na+ AND Cl− IONS IN TIP3P WATER MODEL

We used the TIP3P model in the simulation of Na+ and Cl− ions in liquid water. The radial distribution function was computed to analyze the structure of water and the hydration shells formed around of the Na+ and Cl− ions. We performed simulations with the molecular dynamics package LAMMPS. The main aspects of the physical properties of water related to its atomic structure were also studied. Analysis of the values of the radial distribution function, showed the presence of two peaks, indicating short-range order for liquid water. Through computer experiments the dependence were obtained of the structure of the hydration shells on the temperature

Atomistic simulation of the premelting of iron and aluminum: Implications for high-pressure melting-curve measurements

Using atomistic simulations we show the importance of the surface premelting phenomenon for the melting-curve measurements at high pressures. The model under consideration mimics the experimental conditions deployed for melting studies with diamond-anvil cells. The iron is considered in this work because of the long-standing discrepancies in its melting-curve measurements and its geophysical significance. Results for aluminum are presented for comparison as an opposite case. We calculate the premelting magnitude at different pressures and temperatures and show its influence on the surface roughness that can mislead the experimental determination of the onset of melting in diamond-anvil cells

Toward Determination of the New Hydrogen Hydrate Clathrate Structures

Recently, a new phase of hydrogen hydrates has been observed at ∼5–7 kbar and ∼170–250 K. X-ray diffraction patterns do not allow determination of its structure unambiguously. In this work, we perform classical molecular dynamics simulation of hydrogen hydrates and select two possible structures. One of these structures is not a typical clathrate and has never been observed for hydrates. In this study, we pay special attention to the choice of the model parameters in order to reveal the corresponding sensitivity of the results

Comparison of neutron induced fission and capture in Np-237 and Pu-239 irradiated in QUINTA assembly with 660 MeV proton beam

Two Np-237 samples and one Pu-239 were irradiated in spallation neutrons produced in ADS setup QUINTA. The accelerated beam consisted of protons of energy 660 MeV. The method was based on gamma-ray spectrometry measurement. During analysis of the spectra several fission products and one actinide were identified. Fission product activities gave the number of fissions. The actinide (Np-238), a result of neutron capture by Np-237 gave the number of captures. In a similar manner the number of fissions in Pu-239 was determined. The Pu-240, a product of neutron capture by Pu-239, activity was impossible to measure

Comparison of neutron induced fission and capture in Np-237 and Pu-239 irradiated in QUINTA assembly with 660 MeV proton beam

Two Np-237 samples and one Pu-239 were irradiated in spallation neutrons produced in ADS setup QUINTA. The accelerated beam consisted of protons of energy 660 MeV. The method was based on gamma-ray spectrometry measurement. During analysis of the spectra several fission products and one actinide were identified. Fission product activities gave the number of fissions. The actinide (Np-238), a result of neutron capture by Np-237 gave the number of captures. In a similar manner the number of fissions in Pu-239 was determined. The Pu-240, a product of neutron capture by Pu-239, activity was impossible to measure

Theoretical Study of Electronic Structure of Charged Fullerenes

The properties of excited short-living electron quantum levels of positively charged C60+Z fullerenes are numerically investigated with the help of the density functional theory (DFT) packages Quantum Espresso, ORCA, and VASP. Earlier, the existence of the volume-localized electron states for neutral and charged fullerenes was demonstrated analytically by making use of the model potential approach based on the unique quasispherical geometrical shape of C60. Here, we revisit this issue by verifying numerically the existence of volume-localized states and by calculating physical parameters of all electronic states with a special focus on highly charged fullerene ions. The ionization potentials of C60+Z are calculated and compared with available experimental data. The photoionization cross-sections for neutral fullerene using wave functions are obtained by making use of DFT codes. We demonstrate that lifetimes of excited states vary in the range 10−11÷10−4 s, and for the volume-localized levels, lifetimes are longer than those for the surface-localized states