Gianluca Gregori

Abstract:

We present a novel scheme for modelling quantum plasmas in the warm dense matter (WDM) regime via a hybrid smoothed particle hydrodynamic - molecular dynamic treatment, here referred to as ‘Bohm SPH’. This treatment is founded upon Bohm’s interpretation of quantum mechanics for partially degenerate fluids, does not apply the Born-Oppenheimer approximation, and is computationally tractable, capable of modelling dynamics over ionic timescales at electronic time resolution. Bohm SPH is also capable of modelling non-Gaussian electron wavefunctions. We present an overview of our methodology, validation tests of the single particle case including the hydrogen 1s wavefunction, and comparisons to simulations of a warm dense hydrogen system performed with wave packet molecular dynamics.

Abstract:

Complex multiscale flows associated with instabilities and turbulence are commonly induced under High Energy Density (HED) conditions, but accurate measurement of their transport properties has been challenging. X-ray Photon Correlation Spectroscopy (XPCS) with coherent X-ray sources can, in principle, probe material dynamics to infer transport properties using time autocorrelation of density fluctuations. Here we develop a theoretical framework for utilizing XPCS to study material diffusivity in multiscale flows. We extend single-scale shear flow theories to broadband flows using a multiscale analysis that captures shear and diffusion dynamics. Our theory is validated with simulated XPCS for Brownian particles advected in multiscale flows. We demonstrate the versatility of the method over several orders of magnitude in timescale using sequential-pulse XPCS, single-pulse X-ray Speckle Visibility Spectroscopy (XSVS), and double-pulse XSVS.

Abstract:

We extract electron transport properties from atomistic simulations of a two-component plasma by mapping the long-wavelength behavior to a two-fluid model. The mapping procedure is performed via Markov Chain Monte Carlo sampling over multiple spectra simultaneously. The free-electron dynamic structure factor and its properties have been investigated in the hydrodynamic formulation to justify its application to the long-wavelength behavior of warm dense matter. We have applied this method to warm dense hydrogen modeled with wave packet molecular dynamics and showed that the inferred electron transport properties are in agreement with a variety of reference calculations, except for the electron viscosity, where a substantive decrease is observed when compared to classical models.