Performance of state-of-the-art force fields for atomistic simulations of silicon at high electronic temperatures

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Intensive femtosecond laser pulses or ion bombardment drives Silicon (Si) into a nonequilibrium state with hot electrons and cold ions. Since ab initio molecular dynamics (MD) simulations can only deal with at most 103 atoms, an analytical interatomic potential (or force field) is necessary for performing large-scale simulations describing Si in nonequilibrium. We recently constructed a potential for Si at high electronic temperatures Te’s, which was developed from ab initio MD simulations. In this study, we analyze the performance of this potential compared to other available Te-dependent Si potentials and to some widely used ground state Si potentials, which were adapted to nonequilibrium by fitting their parameters to ab initio MD simulations. We analyze the ability for reproducing nonthermal effects like thermal phonon squeezing and ultrafast melting in bulk Si as well as the expansion due to bond softening of a thin Si film. Our results show that the available Te-dependent potentials cannot quantitatively describe the latter. A much better description is given by the potentials with parameters fitted to ab initio MD simulations. Our proposed potential gives the best description among the studied ones, since its analytical shape was optimized for the ground and the laser excited state.