The molecular dynamics method has been applied to the simulation of the fast-ion conductor SrCl
2
. Calculations have been done at increasing temperatures from low temperatures through the normal and high-conductivity regions into the melt. Because of the periodic boundary conditions imposed and the size of the simulation sample (324 ions), the minimum defect concentration of anion Frenkel defects that can exist in the steady state is 1/216 defects per anion lattice site. At low temperatures Frenkel defects introduced into the initial configuration are eliminated, but at higher temperatures Frenkel defects form spontaneously on the anion sublattice. Anions move primarily in <1 0 0> directions by the vacancy mechanism, although more rarely <1 1 0> jumps also occur. At intermediate temperatures interstitials were observed to make non-collinear interstitialcy jumps, but at higher temperatures the motion of interstitials makes little contribution to mass transport. The vacancies appear to be very mobile and interstitials have little or no chance to move before being annihilated by a wandering vacancy. The picture is thus one of a highly dynamic system in which individual defects do not survive for long. However, it must be recognized that the rigid-ion potential used has its limitations and may overemphasize to some extent the vacancy mobility. There is so much motion on the anion sublattice at temperatures close to melting that various indicators such as the anion–anion radial distribution function, the individual ion displacements in a fixed time, and the anion self-correlation function are quite similar below and above the melting temperature. In this sense therefore, the applied description of sublattice melting does not seem to be inappropriate. However, periodic structure is still recognizable on the anion sublattice until it also disappears on the cation sublattice. The small sample molecular dynamics simulation does not predict defect clustering; this is probably because of limitations of the method and so our results are not necessarily in conflict with recent quasi-elastic neutron scattering results.
Polymer and Water Dynamics in Poly(vinyl alcohol)/Poly(methacrylate) Networks. A Molecular Dynamics Simulation and Incoherent Neutron Scattering Investigation