11 research outputs found
Momentum distribution function and short-range correlations of the warm dense electron gas -- ab initio quantum Monte Carlo results
In a classical plasma the momentum distribution, , decays
exponentially, for large , and the same is observed for an ideal Fermi gas.
However, when quantum and correlation effects are relevant simultaneously, an
algebraic decay, has been predicted. This is of
relevance for cross sections and threshold processes in dense plasmas that
depend on the number of energetic particles. Here we present extensive
\textit{ab initio} results for the momentum distribution of the nonideal
uniform electron gas at warm dense matter conditions. Our results are based on
first principle fermionic path integral Monte Carlo (CPIMC) simulations and
clearly confirm the asymptotic. This asymptotic behavior is directly
linked to short-range correlations which are analyzed via the on-top pair
distribution function (on-top PDF), i.e. the PDF of electrons with opposite
spin. We present extensive results for the density and temperature dependence
of the on-top PDF and for the momentum distribution in the entire momentum
range
Prediction of a roton-type feature in warm dense hydrogen
In a recent Letter [T. Dornheim \textit{et al.}, Phys. Rev. Lett.
\textbf{121}, 255001 (2018)], it was predicted on the basis of \textit{ab
initio} quantum Monte Carlo simulations that, in a uniform electron gas, the
peak of the dynamic structure factor exhibits an
unusual non-monotonic wave number dependence, where , at
intermediate , under strong coupling conditions. This effect was
subsequently explained by the pair alignment of electrons %at an intermediate
range of wave numbers [T. Dornheim \textit{et al.}, Comm. Phys. \textbf{5}, 304
(2022)]. Here we predict that this non-monotonic dispersion resembling the
roton-type behavior known from superfluids should be observable in a dense,
partially ionized hydrogen plasma. Based on a combination of path integral
Monte Carlo simulations and linear response results for the density response
function, we present the approximate range of densities, temperatures and wave
numbers and make predictions for possible experimental observations
Günter Kelbg, the Kelbg potential and its impact on quantum plasma theory
Günter Kelbg did remarkable early work in the field of quantum statistical physics, in particular for dense quantum plasmas. In 2022 we celebrated his 100th birthday. On this occasion, we give a brief overview of his main scientific achievements in the field of quantum plasmas, complemented by some biographical background of his research and teaching environment at Rostock University. Kelbg's main achievement is the derivation of a regularized quantum pair potential. We demonstrate that it is still of high relevance for molecular dynamics and quantum Monte Carlo simulations of dense plasmas.Deutsche Forschungsgemeinschaft
http://dx.doi.org/10.13039/501100001659Peer Reviewe
Momentum distribution function and short-range correlations of the warm dense electron gas: Ab initio quantum Monte Carlo results
In a classical plasma the momentum distribution, , decays exponentially, for large k, and the same is observed for an ideal Fermi gas. However, when quantum and correlation effects are relevant simultaneously, an algebraic decay, has been predicted. This is of relevance for cross sections and threshold processes in dense plasmas that depend on the number of energetic particles. Here we present extensive ab initio results for the momentum distribution of the nonideal uniform electron gas at warm dense matter conditions. Our results are based on first principle fermionic path integral Monte Carlo (CPIMC) simulations and clearly confirm the asymptotic. This asymptotic behavior is directly linked to short-range correlations which are analyzed via the on-top pair distribution function (on-top PDF), i.e., the PDF of electrons with opposite spin. We present extensive results for the density and temperature dependence of the on-top PDF and for the momentum distribution in the entire momentum range
Permutation blocking path integral Monte Carlo approach to the uniform electron gas at finite temperature
The early Upper Palaeolithic of the Tunka rift valley, Lake Baikal region, Siberia
This paper presents recent results of geological and archaeological research at Late Pleistocene sites in the Tunka rift valley (Lake Baikal region, southern Siberia), including new radiocarbon dating of the Palaeolithic layers at Bol'shoi Zangisan, Slavin Yar and Tuyana. The sites range in age from ?26 to 45 ka 14C BP and represent the earliest evidence of human habitation in the area. Numerous faunal remains have also been identified in the archaeological horizons from which palaeoenvironmental conditions can be reconstructed. These data also provide important new information about the age, context, and development of an early microlithic industry in the Tunka-Pribaikal'e region during the late Karginskii interstadial, attributed to Marine Isotope Stage 3 (MIS3). Although further research is needed to verify the reconstructed site age models, archaeological evidence recovered at Tuyana and Bol'shoi Zangisan represent among the oldest known occurrences of microcore-microblade technology in North Asi
First principles simulations of dense hydrogen
International audienceAccurate knowledge of the properties of hydrogen at high compression is crucial for astrophysics (e.g. planetary and stellar interiors, brown dwarfs, atmosphere of compact stars) and laboratory experiments, including inertial confinement fusion. There exists experimental data for the equation of state, conductivity, and Thomson scattering spectra. However, the analysis of the measurements at extreme pressures and temperatures typically involves additional model assumptions, which makes it difficult to assess the accuracy of the experimental data. rigorously. On the other hand, theory and modeling have produced extensive collections of data. They originate from a very large variety of models and simulations including path integral Monte Carlo (PIMC) simulations, density functional theory (DFT), chemical models, machine-learned models, and combinations thereof. At the same time, each of these methods has fundamental limitations (fermion sign problem in PIMC, approximate exchange-correlation functionals of DFT, inconsistent interaction energy contributions in chemical models, etc.), so for some parameter ranges accurate predictions are difficult. Recently, a number of breakthroughs in first principle PIMC and DFT simulations were achieved which are discussed in this review. Here we use these results to benchmark different simulation methods. We present an update of the hydrogen phase diagram at high pressures, the expected phase transitions, and thermodynamic properties including the equation of state and momentum distribution. Furthermore, we discuss available dynamic results for warm dense hydrogen, including the conductivity, dynamic structure factor, plasmon dispersion, imaginary-time structure, and density response functions. We conclude by outlining strategies to combine different simulations to achieve accurate theoretical predictions