A Method for Tractable Dynamical Studies of Single and Double Shock Compression

Abstract

A new multiscale simulation method is formulated for the study of shocked materials. The method combines molecular dynamics and the Euler equations for compressible flow. Treatment of the difficult problem of the spontaneous formation of multiple shock waves due to material instabilities is enabled with this approach. The method allows the molecular dynamics simulation of the system under dynamical shock conditions for orders of magnitude longer time periods than is possible using the popular nonequilibrium molecular dynamics approach. An example calculation is given for a model potential for silicon in which a computational speedup of 10(5) is demonstrated. Results of these simulations are consistent with the recent experimental observation of an anomalously large elastic precursor on the nanosecond time scale.

Nanoscale Molecular Dynamics Simulaton of Shock Compression of Silicon

“…We decided to add SW calculations of uniaxial compression of Si because it was used in recent MD simulations of shock wave propagation in silicon [8]. Inspecting at large compression ratios is the effect of the short-range cutoff used to determine the number of nearest neighbors for each atom.…”

Ultrafast transformation of graphite to diamond: An ab initio study of graphite under shock compression

“…This is accomplished by time-evolving equations of motion for the atoms and volume of the computational of cell to constrain the stress in the propagation direction xx ϵ p to the Rayleigh line and the energy of the system to the Hugoniot energy condition. [17][18][19] In the case of a shock, conservation of mass, momentum, and energy across the shock front leads to the Hugoniot relation E − E 0 = 1 2 ͑p + p 0 ͒͑v 0 − v͒, where E is the energy and v is the volume. A subscript 0 refers to the preshocked state, while quantities without subscripts refer to the postshocked state.…”

“…The multiscale shock technique [17][18][19][20] ͑MSST͒ is a simulation methodology based on the Navier-Stokes equations for compressible flow. Instead of simulating a shock wave within a large computational cell with many atoms, 15 the MSST computational cell follows a Lagrangian point through the shock wave as if the shock were passing over it.…”

Ab Initio Molecular Dynamics Simulations of Water Under Static and Shock Compressed Conditions

“…The MSST [10] maintains the system on both the Rayleigh line p − p 0 = U 2 (v 0 − v)/v 0 , (where U is the shock velocity) and the shock Hugoniot under condition of uniaxial strain of the computational cell. By regulating the strain rate of the computational cell, we guarantee that the (P, T ) thermodynamic states accessed during the shock simulation correspond to a steady macroscopic shock wave.…”

“…The Multi-Scale Shock Technique (MSST) [10,11] can dramatically reduce the number of particles relative to non-equilibrium molecular dynamics (NEMD) methods, while guaranteeing that the simulation converges to the correct thermodynamic end state. The MSST [10] maintains the system on both the Rayleigh line p − p 0 = U 2 (v 0 − v)/v 0 , (where U is the shock velocity) and the shock Hugoniot under condition of uniaxial strain of the computational cell.…”