Bulletin of the American Physical Society
53rd Annual Meeting of the APS Division of Plasma Physics
Volume 56, Number 16
Monday–Friday, November 14–18, 2011; Salt Lake City, Utah
Session YM10: Mini-conference: Dense Quantum Plasma Simulation II |
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Chair: Frank Graziani, Lawrence Livermore National Laboratory Room: 151 ABCG |
Friday, November 18, 2011 9:30AM - 10:00AM |
YM10.00001: Quantum kinetic theory for nonequilibrium electrons: from TDHF to Keldysh Green functions Michael Bonitz, Karsten Balzer, Sebastian Bauch, David Hochstuhl, Sebastian Hermanns In this talk we discuss dense quantum plasmas in nonequilibrium relevant for warm dense matter (WDM) situations. While the ions can usually be treated classically, the electrons require a quantum treatment out of equilibrium. We first present an overview on the results of quantum kinetic theory for modeling the electron dynamics in a time-dependent electric field in a homogeneous plasma [1,2]. The basis is provided by nonequilibrium Greens function which can be computed directly or used to derive an equation of motion for the Wigner distribution. Finally, we present recent results for excitation and relaxation dynamics of electrons in atoms subject to strong laser fields [3] and discuss prospects for WDM applications. \\[4pt] [1] M. Bonitz, ``Quantum Kinetic Theory,'' Teubner, Stuttgart, Leipzig 1998. [2] ``Introduction to Computational Methods for Many-Body Physics,'' M. Bonitz and D. Semkat (eds.), Rinton Press, Princeton 2006. [3] K. Balzer, S. Bauch and M. Bonitz, Phys. Rev. A 82, 033427 (2010). [Preview Abstract] |
Friday, November 18, 2011 10:00AM - 10:30AM |
YM10.00002: The Multilayer Multiconfiguration Time-Dependent Hartree Theory Haobin Wang The multilayer multi-configuration time-dependent Hartree (ML-MCTDH) theory is a powerful tool for carrying out wave packet propagation. This rigorous, variational quantum approach is based on an efficient representation of the functional via several dynamically contracted layers, and thus applicable to systems with many degrees of freedom. The presentation gives an overview on the general derivation of the theory, the scaling of the method for model problems, and examples of application to electron transfer processes in the condensed phase. Generalizations of the theory to treat identical fermion/boson systems will also be presented. [Preview Abstract] |
Friday, November 18, 2011 10:30AM - 10:45AM |
YM10.00003: Temperature-Dependent Behavior of Confined Many-electron Systems in the Hartree-Fock Approximation Travis Sjostrom, Frank Harris, Samuel Trickey Many-electron systems at substantial finite temperatures and densities present a major challenge to density functional theory. Very little is known about the free-energy behavior over the temperature range of interest, for example, in the study of warm dense matter. As a result, it is difficult to assess the validity of proposed approximate free-energy density functionals. Here we address, at least in part, this need for detailed results on well-characterized systems for purposes of testing and calibration of proposed approximate functionals. We present results on a comparatively simple, well-defined, but computationally feasible model, namely thermally occupied Hartree-Fock states for eight one-electron atoms at arbitrary positions in a hard-walled box. We discuss the main technical tasks (defining a suitable basis and evaluation of the required matrix elements) and discuss the physics which emerges from the calculations. In addition the Hartree-Fock results are compared directly to approximate density functional results including finite temperature orbital-free kinetic and exchange functionals. [Preview Abstract] |
Friday, November 18, 2011 10:45AM - 11:15AM |
YM10.00004: Kinetic theory molecular dynamics for hot, dense plasmas M.S. Murillo, C.A. Fichtl, F.R. Graziani, J. Glosli, J. Bauer Plasma simulation methods can be categorized by the degree to which they treat the time dependence of the electrons. Common methods make a Born-Oppenheimer approximation in which the electronic structure is computed for fixed ions. However, many applications, such as energy exchange processes, require explicit treatment of the electron dynamics. As such, we have developed a new method that retains full quantal electron dynamics. We take advantage of the fact that electrons are typically weakly-to-moderately coupled, but degenerate, whereas the ions are typically strongly coupled and classical. This suggests a hybrid method in which we solve for the electrons using a quantum kinetic theory for moderately-coupled, degenerate electrons and a full molecular dynamics approach is used for the ions; we refer to our method as ``Kinetic Theory Molecular Dynamics.'' This computational approach, and its associated numerical implementation, will be described using a mean-field Wigner kinetic approach coupled to ion dynamics. The non-linear interactions that involve the electrons, which populate a time-dependent Fermi-Dirac, are computed using a modified PIC approach. Extensions to this capability will be discussed as well as numerous examples, such as non-linear waves and instabilities, algorithms beyond mean-field, and its use as a tool for understanding dense fusion plasmas. [Preview Abstract] |
Friday, November 18, 2011 11:15AM - 11:45AM |
YM10.00005: Dynamical Screening Approach to Strongly Correlated Multi-Component Plasmas Patrick Ludwig, Michael Bonitz, James Dufty A key problem in the description of nonideal, multi-component plasmas is the drastic difference in the r,t-scales. In dusty plasma physics, this problem has been effectively tackled by the 'Dynamical Screening Approach' (DSA), which allows for an accurate description of essential equilibrium and non-equilibrium plasma properties including screening, wakefield oscillations, ion and electron thermal effects as well as collisional and Landau damping [1,2]. Here, the DSA is extended to non-equilibrium situations in partially ionized Warm Dense Matter, where a full dynamic treatment of the pair correlations of the heavy particles is crucial. Considering the strongly coupled ions as classical (or weakly degenerate) and the electrons as quantum degenerate but only weakly correlated, the ion dynamics will be studied on first principles by classical Langevin Dynamcis simulations, while the electrons are treated fully quantum-mechanically taking into account their dynamical screening of the ion-ion interaction in linear response on the basis of an extended Mermin formula [3].\\[4pt] [1] M. Lampe et al., IEEE Trans. Plasma Sci. \textbf{33}, 57 (2005)\\[0pt] [2] P. Ludwig, W.J. Miloch, H. K\"ahlert, and M. Bonitz, to be published (2011)\\[0pt] [3] P. Ludwig, M. Bonitz, H. K\"ahlert, and J.W. Dufty, J. Phys. Conf. Series \textbf{220}, 012003 (2010) [Preview Abstract] |
Friday, November 18, 2011 11:45AM - 12:00PM |
YM10.00006: Calculation of Transport Coefficients in Dense Plasma Mixtures T. Haxhimali, W.H. Cabot, K.J. Caspersen, J. Greenough, P.L. Miller, R.E. Rudd, E.R. Schwegler We use classical molecular dynamics (MD) to estimate species diffusivity and viscosity in mixed dense plasmas. The Yukawa potential is used to describe the screened Coulomb interaction between the ions. This potential has been used widely, providing the basis for models of dense stellar materials, inertial confined plasmas, and colloidal particles in electrolytes. We calculate transport coefficients in equilibrium simulations using the Green- Kubo relation over a range of thermodynamic conditions including the viscosity and the self - diffusivity for each component of the mixture. The interdiffusivity (or mutual diffusivity) can then be related to the self-diffusivities by using a generalization of the Darken equation. We have also employed non-equilibrium MD to estimate interdiffusivity during the broadening of the interface between two regions each with a high concentration of either species. Here we present results for an asymmetric mixture between Ar and H. These can easily be extended to other plasma mixtures. A main motivation for this study is to develop accurate transport models that can be incorporated into the hydrodynamic codes to study hydrodynamic instabilities. *This work was performed under the auspices of the US Dept. of Energy by Lawrence Livermore National Security, LLC under Contract DE-AC52-07NA27344. [Preview Abstract] |
Friday, November 18, 2011 12:00PM - 12:15PM |
YM10.00007: Semiclassical Simulation of Electron Scattering in Attractive Coulomb Potentials Andreas Markmann, Frank Graziani, Victor Batista We study the performance of semiclassical dynamics simulations of electron scattering in the Wigner-transform time-dependent picture at few attractive Coulomb potentials and a two-slit potential. Heisenberg uncertainty and interference are compared to exact quantum dynamics. Serious numerical problems typically arise in classical and semiclassical simulations involving Coulomb potentials when particles approach each other and potential gradients (or accelerations) diverge. We introduce an accurate and efficient algorithm for dynamics simulations of particles with attractive potentials developed within the multi-institutional Cimarron Project. Rather than avoiding the singularity problem by using a pseudopotential, the algorithm predicts the outcome of close encounter two-body collisions for the true Coulomb potential by solving the Kepler problem analytically and corrects the trajectory for multiscattering with other particles in the system by using standard numerical techniques (e.g., velocity Verlet, or Gear Predictor corrector algorithms). [Preview Abstract] |
Friday, November 18, 2011 12:15PM - 12:30PM |
YM10.00008: Nonlinear plasma waves and wavebreaking in quantum plasmas Hans-Joerg Kull Large amplitude plasma waves are commonly excited in laser-plasma interactions. One of the basic features of nonlinear plasma waves is wavebreaking when a critical wave amplitude is exceeded. The wavebreaking amplitude was first derived by Dawson for cold plasmas [1]. Later this criterion was generalized to thermal and relativistic plasmas by various authors [2-3]. In the present work, we consider the wavebreaking limit in warm dense matter. The basic quantum kinetic equation is the quantum Vlasov equation. We propose a numerical method that solves the set of quantum Vlasov-Maxwell equations with the same efficiency as classical particle-in-cell (PIC) simulations. The basic concept of this method consists in a representation of the ensemble by a set of carrier-envelope waves and a propagation of these waves in their rest frames by the time dependent Schr\"odinger equation. Linear dispersion relations and Landau damping rates can be accurately reproduced by this method. Wavebreaking amplitudes in quantum plasmas are obtained and compared to theoretical results.\\[4pt] [1] J.M. Dawson, Phys. Rev. 113, 383 (1959).\\[0pt] [2] T.P. Coffey, Phys. Fluids 14, 1402 (1971).\\[0pt] [3] T. Katsouleas and W.~B. Mori, Phys. Rev. Lett. 61, 90 (1988). [Preview Abstract] |
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