Computational approaches to the dynamics of ions and electrons in materials under extreme conditions

Recent computational approaches to the atomic scale simulation of materials under extreme conditions are presented, with an emphasis on some tools relevant to the study of both shock and irradiation response, i.e. that are useful to describe chemical reactions or electronic excitations. For reactivity, recently introduced analytic reactive force fields are outlined. An alternative formalism including electronic degrees of freedom through hybrid atomic orbitals and providing a satisfactory description of the charge distribution upon homolytic dissociation processes is put forward. Preliminary results are presented to illustrate this electron distribution model. Although parameterized only against ab initio data calculated on equilibrium molecular structures, the latter yields consistent atomic charges for transition state structures and neutral homolysis products. Finally, an attempt at including the electron dynamics in shock wave simulations is outlined.