Radiation damage is traditionally modelled using cascade simulations, and the effect of inelastic scattering by electrons, if included, is introduced via a friction term in the equation of motion. We have developed a model in which the molecular dynamics simulation is coupled to a model for the electronic energy, which evolves via the heat diffusion equation. Energy lost by the atoms, due electronic stopping or electron-ion interactions, is input to the electronic system via a source term in the diffusion equation. Energy is fed back to the atomic system from the hot electrons by means of a Langevin thermostat, which depends on the local electronic temperature. Results of the model are presented for 10 keV cascades in Fe.

A generic method for producing potentials to model organic-mineral systems is proposed. The method uses existing potentials for the components of the system and produces cross-term potentials between these components. The existing potentials are fitted to known mineral structures modeled with charges that mimic the Coulombic potential at the organic-mineral interface. The method has been applied to supply a set of potentials to model calcite biomineralization, including water-calcite, bicarbonate ions, and a set of organic functional groups with calcite. Tests comparing the results from ab initio and other potential-based calculations demonstrate that the new potential set is reliable and accurate.

Swift heavy ions cause material modification along their tracks, changes primarily due to their very dense electronic excitation. The available data for threshold stopping powers indicate two main classes of materials. Group I, with threshold stopping powers above about 10 keV nm(-1), includes some metals, crystalline semiconductors and a few insulators. Group II, with lower thresholds, comprises many insulators, amorphous materials and high T(c) oxide superconductors. We show that the systematic differences in behaviour result from different coupling of the dense excited electrons, holes and excitons to atomic (ionic) motions, and the consequent lattice relaxation. The coupling strength of excitons and charge carriers with the lattice is crucial. For group II, the mechanism appears to be the self-trapped exciton model of Itoh and Stoneham (1998 Nucl. Instrum. Methods Phys. Res. B 146 362): the local structural changes occur roughly when the exciton concentration exceeds the number of lattice sites. In materials of group I, excitons are not self-trapped and structural change requires excitation of a substantial fraction of bonding electrons, which induces spontaneous lattice expansion within a few hundred femtoseconds, as recently observed by laser-induced time-resolved x-ray diffraction of semiconductors. Our analysis addresses a number of experimental results, such as track morphology, the efficiency of track registration and the ratios of the threshold stopping power of various materials.