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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.