Molecular dynamics simulations of the initial stages of the spall process in single nanocrystals and polynanocrystals of copper are performed. The simulations show that void nucleation in copper polynanocrystals occurs predominantly along the grain boundaries, whereas voids are formed at stacking fault intersections in copper monocrystals. The calculated spall strengths of single-crystal copper at strain rates of $2-4\times {10}^9{\mathrm{s}}^{-1}$ are consistent with existing experimental data, and the polynanocrystal spall strength is found to increase rapidly at rates around ${10}^9{\mathrm{s}}^{-1}$ up to the theoretical ultimate spall strength of $22.5\mathrm{GPa}$ at about $3\times {10}^9{\mathrm{s}}^{-1}$.

Density-functional theory is used to calculate unit-cell energies of $\alpha \text{-Pu}$ and $\delta \text{-Pu}$ 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 $\text{exp}-6$ 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 $\delta \text{-Pu}$ 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 $\delta \text{-Pu}$ 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.

The paper presents a review and comparative analysis of several algorithms for the recognition of crystal structures and defects of various types used in molecular dynamics simulations of materials. A new algorithm called the adaptive template analysis is suggested. Unlike the other algorithms, it is iterative. The algorithms considered were tested in molecular dynamics calculations taking into account temperature changes and high-rate deformation in shock waves.