title: Electronic excitations and their effect on the interionic forces in simulations of radiation damage in metals.
abstract: Using time-dependent tight-binding simulations of radiation damage cascades in a model metal we directly investigate the nature of the excitations of a system of quantum mechanical electrons in response to the motion of a set of classical ions. We furthermore investigate the effect of these excitations on the attractive electronic forces between the ions. We find that the electronic excitations are well described by a Fermi-Dirac distribution at some elevated temperature, even in the absence of the direct electron-electron interactions that would be required in order to thermalize a non-equilibrium distribution. We explain this result in terms of the spectrum of characteristic frequencies of the ionic motion. Decomposing the electronic force into four well-defined components within the basis of instantaneous electronic eigenstates, we find that the effect of accumulated excitations in weakening the interionic bonds is mostly (95%) accounted for by a thermal model for the electronic excitations. This result justifies the use of the simplifying assumption of a thermalized electron system in simulations of radiation damage with an electronic temperature dependence and in the development of temperature-dependent classical potentials.
authors.affiliation: Department of Physics, Imperial College London, London SW7 2AZ, UK.
authors.forename: C P
authors.initials: CP
authors.lastname: Race
authors.forename: D R
authors.initials: DR
authors.lastname: Mason
authors.forename: A P
authors.initials: AP
authors.lastname: Sutton