Nanoscale Modeling of Shock-Induced Deformation of Diamond

Molecular dynamics (MD) simulations of shock-induced deformations in diamond were performed using a reactive bond order (REBO) potential. A splitting of shock wave structure into elastic and crystal deformation fronts was observed in the [110] and [111] crystallographic directions above piston velocity thresholds of up ≈ 1.8 and 2.5 km/s, respectively. The crystal lattice response in a split two-wave regime consists of the relative movement of {111} planes in the diamond crystal and has different structural character for [110] and [111] shock waves. The strain produced by a [110] shock wave occurs only along one of the transverse crystalline directions, whereas in the [111] case crystal deformation involves the movement of the atoms in both transverse directions. To gain insight into the atomistic mechanisms of orientational dependence of shock compression of crystals, we have investigated in detail the constitutive stress-strain relationships under static uniaxial compression. The REBO potential gives a reasonably good description of stresses and energetics under moderate uniaxial compressions corresponding to an elastic shock wave regime. However, under compressions higher than 10% ([110] case) and 20% ([111] case) the REBO potential shows deficiencies in the quantitative description of stress response that might affect the MD picture of shock wave deformations in diamond.