Bulletin of the American Physical Society
2007 APS March Meeting
Volume 52, Number 1
Monday–Friday, March 5–9, 2007; Denver, Colorado
Session S23: High Pressure V |
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Sponsoring Units: DCMP Chair: Joel Kresse, Los Alamos National Laboratory Room: Colorado Convention Center 110 |
Wednesday, March 7, 2007 2:30PM - 2:42PM |
S23.00001: Quantum Monte Carlo determination of the equation of state of cubic boron nitride K.P. Esler, B. Militzer, R.E. Cohen The pressure inside a diamond anvil cell is usually determined by measuring the pressure-dependent frequency shift of a small ruby sample or by x-ray diffraction on a small chip of a pressure standard. However, there are no primary pressure standards for the megabar range. Recently, cubic boron nitride (cBN) has been suggested as an accurate pressure gauge.$^1$ Unlike ruby, its structure is highly constrained by symmetry and stable beyond 100 GPa, and it has a well-separated Raman spectrum with sufficient pressure dependence to allow accurate pressure calibration. Its use as a pressure standard requires reliable equation of state (EOS) data. A density functional theory (DFT) calculation of the cBN EOS based on the generalized gradient approximation agrees well with experiment up to 100 GPa, but a calculation that does not depend on an approximate exchange-correlation functional would be desirable. Quantum Monte Carlo (QMC) is a correlated, first-principles simulation method with fewer uncontrolled approximations than DFT methods. We present the results of applying state-of-the-art QMC methods to the bulk cBN solid in order to determine the EOS. \\ \\ \hspace{0.3cm} \mbox{}$^1$ A.F. Goncharov et al., Phys. Rev. B {\bf 72}, 100104R (2005). [Preview Abstract] |
Wednesday, March 7, 2007 2:42PM - 2:54PM |
S23.00002: First-principles study of cubic BC6N: Structural forms and ideal strength Yi Zhang, Hong Sun, Changfeng Chen We present first-principles calculations on the structural forms and ideal strength of cubic BC6N. The calculated ideal tensile and shear strength are lower or comparable to those of c-BN. Our results show that increasing carbon content does not lead to significant enhancement of the idea strength as expected by the conventional wisdom. It can be attributed to the weak C-N bonds that impose a limit on the idea strength. [Preview Abstract] |
Wednesday, March 7, 2007 2:54PM - 3:06PM |
S23.00003: Towards a mulitphase equation of state of Carbon from first principles Alfredo Correa, Lorin Benedict, Eric Schwegler Ab initio molecular dynamics and electronic structure calculation had become one of the most useful tools to investigate properties of materials. Unfortunately these atomistic detailed results are rarely reused in calculations at a higher level of description, such as fluid dynamics and finite elements calculations. In this talk we present a concrete example showing the way that first principles results can be expressed in a way that is useful for hydrodynamics calculations, in particular we show how to build a analytic equation of state for Carbon that involves solid (diamond and BC8) and liquid phases. Applications of this newly obtained equation of state will be presented. This work was performed under the auspices of the U.S. Dept. of Energy at the University of California/Lawrence Livermore National Laboratory under contract no. W-7405-Eng-48. [Preview Abstract] |
Wednesday, March 7, 2007 3:06PM - 3:18PM |
S23.00004: VLab: A Collaborative Grid/Portal System for Computations of Materials Properties at High Pressures and Temperatures Pedro da Silveira, Cesar R. S. da Silva, Renata M. Wentzcovitch We describe the development of a collaborative service-oriented architecture, the VLab, which handles from a single workflow the concurrent and distributed execution of multiple tasks involved in complex sequences of first principles calculations of materials properties at high pressures and temperatures. We demonstrate the usefulness of this system through a consolidated portal interface. [Preview Abstract] |
Wednesday, March 7, 2007 3:18PM - 3:30PM |
S23.00005: Shock-wave propagation in carbon nanotube reinforced a-SiC composites Deepak Srivastava, Maxim Makeev We have performed state-of-the-art large-scale molecular dynamics simulation study of shock-wave propagation in amorphous silicon carbide (a-SiC) and carbon nanotube (CNT) reinforced a-SiC composites. The materials response, shock-wave structure, damage evolution and properties in shock-loaded CNT/a-SiC composites are found to differ significantly from the similar shock wave propagation in pristine a-SiC sample. The effects of CNTs on the shock-wave velocity and profile are investigated and analyzed in detail. In all the considered cases, a significant densification is observed in the shock-loaded regions. In the case of CNTs aligned perpendicular to the impact direction, the shock-wave causes CNTs to collapse, while in the case of CNTs oriented parallel to the impact direction the structure of the CNTs is preserved and a channeling of the resulting compressive wave is observed which leads to material sputtering at the bottom surface. The micro-structural changes in the after shock region will be discussed in this presentation. [Preview Abstract] |
Wednesday, March 7, 2007 3:30PM - 3:42PM |
S23.00006: Molecular Dynamics Simulations of Hypervelocity Impacts Eli T. Owens, Martina E. Bachlechner Outer space silicon solar cells are exposed to impacts with micro meteors that can destroy the surface leading to device failure. A protective coating of silicon nitride will protect against such failure. Large-scale molecular dynamics simulations are used to study how silicon/silicon nitride fails due to hypervelocity impacts. Three impactors made of silicon nitride are studied. Their cross-sectional areas, relative to the target, are as follows: the same as the target, half of the target, and a quarter of the target. Impactor speeds from 5 to 11 km/second yield several modes of failure, such as deformation of the target by the impactor and delimitation of the silicon nitride from the silicon at the interface. These simulations will give a much clearer picture of how solar cells composed of a silicon/silicon nitride interface will respond to impacts in outer space. This will ultimately lead to improved devices with longer life spans. [Preview Abstract] |
Wednesday, March 7, 2007 3:42PM - 3:54PM |
S23.00007: The generation of dissipative structures in solids at high pressures Roger W. Minich, Daniel Orlikowski, Jeff H. Nguyen The recent ability to tailor pressure drives up to and exceeding a Mbar has led to the ability to study the response of materials along different thermodynamic paths that may be significantly different from a Hugoniot. Observations of recent data suggest that a ramped pressure drive generates coherent structures that behave like solitons in the weakly dissipative limit, but later form kinks which localize the dissipation and coalesce into ever increasing larger kinks in time. The experimental observations are discussed in the context of the KdV-Burgers equation and a universal scaling law is proposed in the limit of high dissipation. This work was performed under the auspices of the U.S. Department of Energy by the University of California Lawrence Livermore National Laboratory under contract W-7405-Eng-48. [Preview Abstract] |
Wednesday, March 7, 2007 3:54PM - 4:06PM |
S23.00008: Large scale MD Simulations of the time-resolved optical properties of warm dense metals S. Mazevet, J. Clerouin, L. Soulard Recent experiments on gold suggest that the electrical and optical properties of metals in the warm dense matter regime can be accessed by performing time-resolved measurements after the illumination of a metallic thin film by a short-pulse laser[1]. The non-equilibrium situation created in this experimental setup poses new challenges to simulation methods as the time evolution of the atomic structure needs to be followed as the metal evolves from a solid to a plasma state. We used a combination of {\sl ab-initio} and large scale molecular dynamics simulations to calculate the evolution of the atomic structure, and the electrical conductivity of various metals during the first pico-seconds after a short-pulse laser illumination. \newline \newline [1] K. Widmann, T. Ao, M.E. Foord, D.F. Price, A.D. Ellis, P.T. Springer,and A. Ng, Phys. Rev. Lett. {\bf 92}, 125002 (2004). [Preview Abstract] |
Wednesday, March 7, 2007 4:06PM - 4:18PM |
S23.00009: Dynamics of ultracold neutral plasma Lee Collins, Byoungseon Jeon, Joel Kress, Niels Gronbech-Jensen For an ultracold neutral plasma produced by photoionzation of laser-cooled heavy particles, initial expansion behavior was studied with classical molecular dynamics. To investigate huge particle sets under open boundary condition, the TREE method has been implemented and Rydberg states of low quantum number were studied. We also examined the degree of ion correlation. [Preview Abstract] |
Wednesday, March 7, 2007 4:18PM - 4:30PM |
S23.00010: Hot and Cold Ionization of Strongly Coupled Plasmas Generated by Intense Shock Waves Vladimir Fortov The physical properties of strongly coupled plasmas at high pressures and energy densities are analyzed in a broad region of parameters. The theoretical and experimental methods of non-ideal plasma investigations are discussed. Main attention is paid to the dynamical methods. Intense shock, rarefaction, and radiative waves in solid and porous samples, and electrical explosion were used for generation of high density plasmas at extremely high pressure. The pressure ionization plasma phenomena in hydrogen, helium, noble gases, iodine, silica, sulfur, H2O, fullerenes and some metals are analyzed on the base of multiple shock wave experiments. The data obtained were described by the non-ideal plasma model taking into account increase of charge carrier number as a result of ``temperature'' and ``pressure'' ionization. In contrast to these experiments the multiple shock compression of solid Li, Ca and Na shows strong modification of electron plasma energy spectrum and as a result of that - dielectrization of these elements at megabars. The ``plasma'' phase transition phenomena are analyzed on the base of shock experiments and quantum Monte-Carlo simulations. [Preview Abstract] |
Wednesday, March 7, 2007 4:30PM - 4:42PM |
S23.00011: Relaxation of laser-induced two component plasma Byoungseon Jeon, Lee Collins, Joel Kress, Niels Gronbech-Jensen In inertial-confined fusion plasmas, the ions and electrons can exist in a non-equilibrium state. Using classical molecular dynamics, we have studied a two-temperature plasma under extreme conditions and determined system properties. The temperature relaxation rate and diffusion coefficients of each species were found, and the results were compared with the Spitzer and other relaxation formulae. [Preview Abstract] |
Wednesday, March 7, 2007 4:42PM - 4:54PM |
S23.00012: First Principles Molecular Dynamics Simulations of Diopside Liquid at High Pressure Ni Sun, Lars Stixrude, Bijaya Karki Diopside (CaMgSi$_{2}$O$_{6})$ is a major component of basalt; the high-pressure end members, Mg-perovskite (MgSiO$_{3})$ and Ca-perovskite (CaSiO$_{3})$, make up more than 80 {\%} of the lower mantle. Despite its importance, most studies of diopside liquid have been performed at relatively low pressures and temperatures. In this study, we investigated CaMgSi$_{2}$O$_{6}$ liquid at lower mantle conditions by first principles molecular dynamics (FPMD) simulations based on density functional theory. The average Si-O coordination number increases nearly linearly from 4 to 6 with two-fold compression. The structure shows evidence of incipient exsolution with non-random clustering of Mg and Ca ions. Our results are well fitted by Mie-Gr\"{u}neisen equation of state with a Gr\"{u}neisen parameter that increases on compression. The variation of the diffusion coefficient with pressure and temperature is captured by the Arrhenius relation with activation energy and volume E* = 1.2 eV and V* = 1.25 {\AA}$^{3}$. The electronic properties of the CaMgSi$_{2}$O$_{6}$ liquid phase are similar as those of the MgSiO$_{3}$ liquid: there is no band gap and an extra peak appears at the Fermi level at low pressure. [Preview Abstract] |
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