Anomalous sound propagation and slow kinetics in dynamically compressed amorphous carbon

We have performed molecular-dynamics simulations of dynamic compression waves propagating through amorphous carbon using the Tersoff potential and find that a variety of dynamic compression features appear for two different initial densities. These features include steady elastic shocks, steady chemically reactive shocks, unsteady elastic waves, and unsteady chemically reactive waves. We show how these features can be distinguished by analyzing time-dependent propagation speeds, time-dependent sound speeds, and comparison to multiscale shock technique (MSST) simulations. Understanding such features is a key challenge in quasi-isentropic experiments involving phase transformations. In addition to direct simulations of dynamic compression, we employ the MSST and find agreement with the direct method for this system for the shocks observed. We show how the MSST can be extended to include explicit material viscosity and demonstrate on an amorphous Lennard-Jones system.