The uniform electron gas (UEG) at finite temperature is of key relevance for many applications in dense plasmas, warm dense matter, laser excited solids and much more. Accurate thermodynamic data for the UEG are an essential ingredient for many-body
theories, in particular, density functional theory. Recently, first-principle restricted path integral Monte Carlo results became available which, however, due to the fermion sign problem, had to be restricted to moderate degeneracy, i.e. low to moderate densities with $r_s={bar r}/a_B gtrsim 1$. Here we present novel first-principle configuration PIMC results for electrons for $r_s leq 1$. We also present quantum statistical data within the $e^4$-approximation that are in good agreement with the simulations at small to moderate $r_s$.
We evaluate various analytical models for the electron-ion energy transfer and compare the results to data from molecular dynamics (MD) simulations. The models tested includes energy transfer via strong binary collisions, Landau-Spitzer rates with di
fferent choices for the cut-off parameters in the Coulomb logarithm, rates based on Fermis golden rule (FGR) and theories taking coupled collective modes (CM) into account. In search of a model easy to apply, we first analyze different approximations of the FGR energy transfer rate. Then we investigate several numerical studies using MD simulations and try to uncover CM effects in the data obtained. Most MD data published so far show no distinct CM effects and, thus, can be interpreted within a FGR or binary collision approach. We show that this finding is related to the parameter regime, in particular the initial temperature difference, considered in these investigations.
Creating non-equilibrium states of matter with highly unequal electron and lattice temperatures allows unsurpassed insight into the dynamic coupling between electrons and ions through time-resolved energy relaxation measurements. Recent studies on lo
w-temperature laser-heated graphite suggest a complex energy exchange when compared to other materials. To avoid problems related to surface preparation, crystal quality and poor understanding of the energy deposition and transport mechanisms, we apply a different energy deposition mechanism, via laser-accelerated protons, to isochorically and non-radiatively heat macroscopic graphite samples up to temperatures close to the melting threshold. Using time-resolved x ray diffraction, we show clear evidence of a very small electron-ion energy transfer, yielding approximately three times longer relaxation times than previously reported. This is indicative of the existence of an energy transfer bottleneck in non-equilibrium warm dense matter.
We use a two-fluid model combining the quantum Greens function technique for the electrons and a classical HNC description for the ions to calculate the high-density equation of state of hydrogen. This approach allows us to describe fully ionized pla
smas of any electron degeneracy and any ionic coupling strength which are important for the modeling of a variety of astrophysical objects and inertial confinement fusion targets. We have also performed density functional molecular dynamics simulations (DFT-MD) and show that the data obtained agree with our approach in the high density limit. Good agreement is also found between DFT-MD and quantum Monte Carlo simulations. The thermodynamic properties of dense hydrogen can thus be obtained for the entire density range using only calculations in the physical picture.
