Molecular Dynamics Simulations of Inelastic X-Ray Scattering from Shocked Copper*

By taking the spatial and temporal Fourier transforms of the coordinates of the atoms in molecular dynamics simulations conducted using an embedded-atom-method potential, we calculate the inelastic scattering of x-rays from copper single-crystals shocked along [001] to pressures of up to 70 GPa. Above the Hugoniot elastic limit (HEL), we find that the copious stacking faults generated at the shock front introduce strong quasi-elastic scattering (QES) that competes with the inelastic scattering signal, which remains discernible within the first Brillouin zone; for specific directions in reciprocal space outside the first zone, the QES dominates the inelastic signal overwhelmingly. The synthetic scattering spectra we generate from our Fourier transforms suggest that energy resolutions of order 10~meV would be required to distinguish inelastic from quasi-elastic scattering within the first Brillouin zone of shock-loaded copper. We further note that high-resolution inelastic scattering also affords the possibility of directly measuring particle velocities via the Doppler shift. These simulations are of relevance to future planned inelastic scattering experiments at x-ray Free Electron Laser (FEL) facilities.