Tight-Binding Molecular Dynamics of Shock Waves in Methane

The behavior of shock-compressed methane at high temperatures and pressures is studied using nonequilibrium molecular dynamics and linear-scaling tight-binding electronic structure theory in simulations containing as many as 1728 molecules. For certain piston velocities, a chemical dissociation wave evolves that lags behind the compressive shock front. At about 1 ps, the dissociation region consists mainly of molecular hydrogen and hydrocarbon polymers. Shock wave experiments, which access much longer time scales, suggest that the hydrocarbons ultimately decompose into elemental carbon.