Accelerated Molecular Dynamics Simulations of Shock-Induced Chemistry: Application to Liquid Benzene

Shock-induced phenomena in materials occur on timescales that while short may still be beyond the reach of traditional molecular dynamics simulations. The shock-induced chemistry of liquid benzene provides an excellent example of the importance of timescale in shock experiments; reactions are seen at about 13.3 GPa on microsecond timescales in plate impact experiments but it appears inert at up to 20 GPa over 100s of picoseconds during laser-driven shock experiments. We have studied the shock-induced chemistry of liquid benzene using a semiempirical reactive interatomic potential at timescales beyond those routinely accessible to traditional molecular dynamics simulations. We have applied replica-based accelerated molecular dynamics to this system because the initial chemical reactions themselves can be viewed as rare, state-to-state transitions that take place under thermal activation. Replica-based accelerated molecular dynamics enables us to parallelize the simulations in time with no loss of accuracy, provided that transitions (reactions) can be detected reliably. We have simulated the shocked chemical dynamics of benzene on timescales up to 7.7 ns with high parallel efficiency. The simulations show the formation dimers through Diels–Alder condensation. The dimers subsequently condense into larger polymeric structures, in good accord with experiments and quantum chemical data.