Bulletin of the American Physical Society
18th Biennial Intl. Conference of the APS Topical Group on Shock Compression of Condensed Matter held in conjunction with the 24th Biennial Intl. Conference of the Intl. Association for the Advancement of High Pressure Science and Technology (AIRAPT)
Volume 58, Number 7
Sunday–Friday, July 7–12, 2013; Seattle, Washington
Session K3: TM First Principles Methods V |
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Chair: Rudy Magyar, Sandia National Laboratories Room: Fifth Avenue |
Tuesday, July 9, 2013 1:45PM - 2:15PM |
K3.00001: Nitrogen-rich mixtures for high-energy density applications Invited Speaker: Amanuel Teweldeberhan Nitrogen transforms from molecular to polymeric phase at high pressure. Polymeric nitrogen is one of the most studied candidates for high energy density materials. There is an interesting question of whether introducing small amount of impurities can alter the polymerization to lower pressures and lead to enhanced metastabilty. To address this, we have used first-principles density functional theory to study the electronic, structural, and dynamical properties of nitrogen-rich mixtures. We have identified several solid phases for different nitrogen concentrations and investigated the thermodynamic stability of solid and liquid mixtures with respect to their pure components. [Preview Abstract] |
Tuesday, July 9, 2013 2:15PM - 2:30PM |
K3.00002: Achieving accuracy in first-principles calculations at extreme temperature and pressure Ann E. Mattsson, John M. Wills First-principles calculations are increasingly used to provide EOS data at pressures and temperatures where experimental data is difficult or impossible to obtain. The lack of experimental data, however, also precludes validation of the calculations in those regimes. Factors influencing the accuracy of first-principles data include theoretical approximations, and computational approximations used in implementing and solving the underlying equations. The first category includes approximate exchange-correlation functionals and wave equations simplifying the Dirac equation. In the second category are, e.g., basis completeness and pseudo-potentials. While the first category is extremely hard to assess without experimental data, inaccuracies of the second type should be well controlled. We are using two rather different electronic structure methods (VASP and RSPt) to make explicit the requirements for accuracy of the second type. We will discuss the VASP Projector Augmented Wave potentials, with examples for Li and Mo. Sandia National Laboratories is a multi-program laboratory managed and operated by Sandia Corporation, a wholly owned subsidiary of Lockheed Martin Corporation, for the U.S. Department of Energy's National Nuclear Security Administration under contract DE-AC04-94AL85000 [Preview Abstract] |
Tuesday, July 9, 2013 2:30PM - 2:45PM |
K3.00003: Achieving accuracy in first-principles calculations for EOS: basis completeness at high temperatures John M. Wills, Ann E. Mattsson First-principles electronic structure calculations can provide EOS data in regimes of pressure and temperature where accurate experimental data is difficult or impossible to obtain. This lack, however, also precludes validation of calculations in those regimes. Factors that influence the accuracy of first-principles data include (1) theoretical approximations and (2) computational approximations used in implementing and solving the underlying equations. In the first category are the approximate exchange/correlation functionals and approximate wave equations approximating the Dirac equation; in the second are basis completeness, series convergence, and truncation errors. We are using two rather different electronic structure methods (VASP and RSPt) to make definitive the requirements for accuracy of the second type, common to both. In this talk, we discuss requirements for converged calculation at high temperature and moderated pressure. At convergence we show that both methods give identical results. Sandia National Laboratories is a multi-program laboratory managed and operated by Sandia Corporation, a wholly owned subsidiary of Lockheed Martin Corporation, for the U.S. Department of Energy's National Nuclear Security Administration under contract DE-AC04-94AL85000. [Preview Abstract] |
Tuesday, July 9, 2013 2:45PM - 3:00PM |
K3.00004: Z methodology for phase diagram studies: tantalum and platinum as examples Leonid Burakovsky, Dean Preston, Shao Ping Chen, Daniel Sheppard Z methodology is a novel technique for phase diagram studies. It combines direct Z method for the calculation of melting curves, and inverse Z method for the calculation of solid-solid phase boundaries. Relative solid phase stability is studied by comparing melting curves of different solid phases to determine which one is the highest, and thus which of the corresponding solid phases is the most stable. is accomplished using direct Z method. Subsequently, solid-solid phase boundaries can be determined by freezing liquid into the most stable solid phases on both sides of the phase boundary. Inverse Z method represents the implementation of this approach in terms of ab initiomolecular dynamics using VASP package. We will discuss the application of Z methodology to the study of the phase diagrams of tantalum and platinum, and compare our results to the most recent experimental data. [Preview Abstract] |
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