The influence of the electronic specific heat on swift heavy ion irradiation simulations of silicon

The swift heavy ion (SHI) irradiation of materials is often modelled using the two-temperature model. While the model has been successful in describing SHI damage in metals, it fails to account for the presence of a bandgap in semiconductors and insulators. Here we explore the potential to overcome this limitation by explicitly incorporating the influence of the bandgap in the parameterisation of the electronic specific heat for Si. The specific heat as a function of electronic temperature is calculated using finite temperature density functional theory with three different exchange correlation functionals, each with a characteristic bandgap. These electronic temperature dependent specific heats are employed with two-temperature molecular dynamics to model ion track creation in Si. The results obtained using a specific heat derived from density functional theory showed dramatically reduced defect creation compared to models that used the free electron gas specific heat. As a consequence, the track radii are smaller and in much better agreement with experimental observations. We also observe a correlation between the width of the band gap and the track radius, arising due to the variation in the temperature dependence of the electronic specific heat

Domain decomposition of the two-temperature model in ᴅʟ_ᴘᴏʟʏ_4

Including the effects of excited electrons in classical simulations, at the level of the two-temperature model, involves the coupling of a grid-based finite-difference solver for a heat diffusion equation and classical molecular dynamics simulations with an inhomogeneous thermostat. Simulation of large systems requires domain decomposition of both particle-based and grid-based techniques. Starting with the CCP5 flagship code dl_poly_4 as the domain-decomposed molecular dynamics code, we devised a method to divide up temperature grids among processor cores in a similar fashion, including the appropriate communications between cores to deal with boundaries between grid divisions. This article gives the outline of how the domain decomposition of the temperature grids was achieved, as well as some example applications of the two-temperature model implementation in dl_poly_4