No abstract

No abstract

Analysis of phase diagram of beryllium at high pressures and temperatures obtained as a result of ab initio calculations and large scale classical molecular dynamics simulations of beryllium shock loading have shown that the so called cold melting takes place when shock wave propagates through polycrystalline samples. Comparison of ab initio calculation results on sound speed along the Hugoniot with experimental data obtained on Z-machine also evidences for possible manifestation of the cold melting. The last may explain the discrepancy between atomistic simulations and experimental data on the onset of the melting on the Hugoniot.

Density-functional theory is used to calculate unit-cell energies of ␣-Pu and ␦-Pu lattices containing point defects that are manifest in terms of a contaminant He atom. These cell energies are used in the development of a new exp− 6 Pu-He interatomic potential. Molecular-dynamics simulations are conducted to investigate the dynamics of individual He atoms and of a cluster of He atoms in a ␦-Pu lattice. In both cases, the He atoms are shown to precipitate chain reactions involving split interstitial migration of Pu. The rate of this split interstitial migration is calculated. Molecular dynamics is also used to investigate the dynamics of an isolated He bubble in a ␦-Pu lattice. Questions concerning the stability of a He bubble possessing a He-to-vacancy ratio of 3:1 are investigated. Molecular-dynamics simulations investigating the evolution of bubble shape over time are carried out.

No abstract

No abstract

No abstract

Abstract. Theoretical and experimental investigation into properties of condensed matter is one of the mainstreams in RFNC-VNIITF scientific activity. The method of molecular dynamics (MD) is an innovative method of theoretical materials science. Modern supercomputers allow the direct simulation of collective effects in multibillion atom sample, making it possible to model physical processes on the atomistic level, including material response to dynamic load, radiation damage, influence of defects and alloying additions upon material mechanical properties, or aging of actinides. During past ten years, the computer code MOLOCH has been developed at RFNC-VNIITF. It is a parallel code suitable for massive parallel computing. Modern programming techniques were used to make the code almost 100% efficient. Practically all instruments required for modelling were implemented in the code: a potential builder for different materials, simulation of physical processes in arbitrary 3D geometry, and calculated data processing. A set of tests was developed to analyse algorithms efficiency. It can be used to compare codes with different MD implementation between each other.