Bulletin of the American Physical Society
APS March Meeting 2011
Volume 56, Number 1
Monday–Friday, March 21–25, 2011; Dallas, Texas
Session Q31: Focus Session: Materials at High Pressure V: Structure Prediction and Complex Materials |
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Sponsoring Units: DMP GSCCM DCOMP Chair: Salah Boulfelfel, SUNY Stony Brook Room: C145 |
Wednesday, March 23, 2011 11:15AM - 11:51AM |
Q31.00001: Crystal structure prediction using evolutionary algorithms: how to predict large and complex systems Invited Speaker: Evolutionary crystal structure prediction proved to be a powerful approach in discovering new materials. Algorithm USPEX allows one to predict the most stable crystal structure for a given compound without requiring any experimental input. However, certain limitations are encountered for systems with a large number of degrees of freedom and complex energy landscapes. We explore the nature of these limitations and address them with a number of newly developed tools. For large systems a major problem is the lack of diversity. It is countered with modified variation operators that favor atoms with higher local order and a special initialization procedure for the first generation. For complex energy landscapes, the key problem is the possible existence of several energy funnels. To address this problem, we develop an algorithm incorporating the ideas of abstract ``distance'' between structures using the so called ``fingerprint function.'' We will compare the efficiency of the old and new algorithm USPEX for different systems and show that the range of application for algorithm is increased. Some systems, where old algorithm couldn't find a solution are now solvable with the new algorithm. And the speed of finding the solutions for systems with the complicated energy landscape is substantially increased. [Preview Abstract] |
Wednesday, March 23, 2011 11:51AM - 12:03PM |
Q31.00002: Prediction of complex high-pressure M-B crystal structures with an evolutionary algorithm Aleksey Kolmogorov, Sheena Shah, Roxana Margine We have carried out an ab initio ground state search in two binary metal-boron systems using an evolutionary algorithm [1] and identified remarkably complex configurations stabilized at high pressures [2,3]. An alkali-earth metal boride is shown to undergo a structural transformation from a semiconducting to a metallic state while a new semiconducting transition metal boride is stabilized at a composition known to have only metallic ground states. For the proposed candidate materials we calculate the electron-phonon coupling and demonstrate their potential to be phonon-mediated superconductors. \\[4pt] [1] A.N. Kolmogorov, http://maise-guide.org (MAISE) \\[0pt] [2] A. N. Kolmogorov, S. Shah, E. R. Margine, A. F. Bialon, T. Hammerschmidt, R. Drautz, Phys. Rev. Lett. 105, 217003 (2010). \\[0pt] [3] A. F. Bialon, T. Hammerschmidt, R. Drautz, S. Shah, E. R. Margine, A. N. Kolmogorov (submitted) [Preview Abstract] |
Wednesday, March 23, 2011 12:03PM - 12:15PM |
Q31.00003: Structure prediction for molecular crystals using evolutionary algorithms: methodology and applications Qiang Zhu Evolutionary crystal structure prediction proved to be a powerful approach in determining the atomic crystal structure of materials. Here, we present a specifically designed algorithm for the prediction of the structure of molecular crystals. The main feature of this new approach is that each molecule is treated as a whole body, which drastically reduces the search space and improves the efficiency, but necessitates the introduction of new variation operators described here. We illustrate the efficiency of this approach by a search for ice (H2O) structures at zero pressure and temperature, which easily finds the structures of ice Ih and Ic, as well as the thermodynamically stable at these conditions ice XI. We successfully apply this method to finding the hitherto unknown structures of plastic phases of methane at high pressure. These structures are distinguished by an icosahedral packing of the molecules, and are likely candidate solutions for methane A and B. [Preview Abstract] |
Wednesday, March 23, 2011 12:15PM - 12:27PM |
Q31.00004: Burnett-Cattaneo Continuum Theory for Shock Waves B.L. Holian, M. Mareschal, R. Ravelo We model strong shockwave propagation, both in the ideal gas and in the dense Lennard-Jones fluid, using a refinement of earlier work \footnote{B.L. Holian, M. Mareschal, and R. Ravelo, J. Chem. Phys. {\bf 133}, 114502 (2010)}, which accounts for the cold compression by a nonlinear, Burnett-like, strain-rate dependence of the thermal conductivity, and relaxation of temperature components on the hot, compressed side of the shock front. The relaxation of the disequilibrium among the three components of the kinetic temperature, namely, the difference between the temperature in the direction of a planar shock wave and those in the transverse directions, particularly in the region near the shock front, is accomplished by a rigorous application of the Cattaneo-Maxwell relaxation equation to a reference state, namely, the steady shockwave solution of linear Navier-Stokes-Fourier theory, along with the nonlinear Burnett heat-flux term. Our new continuum theory is in nearly quantitative agreement with non-equilibrium molecular-dynamics simulations under strong shockwave conditions. [Preview Abstract] |
Wednesday, March 23, 2011 12:27PM - 12:39PM |
Q31.00005: High-pressure behavior of a novel, nitrogen-rich energetic material R. Stewart McWilliams, Jennifer Ciezak-Jenkins, Yasmin Kadry, Vitaly Prakapenka, Mohammad Mahmood, Alexander Goncharov Energetic materials are of great interest in energy and defense applications. In the search for new energetic materials with improved properties, such as reduced environmental impact, a crystalline solid Triaminoguanidinium 1-methyl-5-nitriminotetrazolate (TAG), C$_{3}$H$_{12}$N$_{12}$O$_{2}$, has recently been synthesized (Klap\"{o}tke et. al. 2008). We have studied the properties of TAG under static compression, and under reaction initiation at high pressure, using Raman and IR spectroscopy and x-ray diffraction. TAG appears to remain a stable, crystalline solid up to at least 35 GPa at room temperature. Laser initiation at 10-15 GPa reveals a rapid self-propagating reaction (deflagration) that consumes the sample, similar to other energetic materials such as nitromethane. Post-initiation products include crystalline molecular nitrogen (delta-phase), and nitrogen crystallites with regular defects. The formation of bulk molecular nitrogen during deflagration - in both phase segregated and impurity-hosting forms - distinguishes TAG from other known energetic materials, and suggests a pathway for the generation of novel phases from element-enriched energetic substances. [Preview Abstract] |
Wednesday, March 23, 2011 12:39PM - 12:51PM |
Q31.00006: High pressure--high temperature studies of ammonia Julius Ojwang, Ryan McWilliams, Alexander Goncharov Raman scattering measurements and x-ray diffraction of ammonia have been made under simultaneous conditions of high temperature and high static pressure in the laser heated diamond anvil cell. The experimental results on phase transitions with pressure increase at room temperature are found to be in accord with previous studies [1]. Pressure was increased up to 52 GPa and temperature ramped up to 2000 K. On increasing temperature at high pressure, strong changes in the ammonia Raman spectra are observed, which could be associated with melting. On melting, ammonia undergoes partial decomposition into nitrogen and hydrogen. We also observed the appearance of new N-H stretch bands at high temperatures which may be related to the formation of new bonds. When quenched back to room temperature the starting phase of solid ammonia is recovered. The shift in frequencies of the vibron bands of nitrogen with pressure shows that it is phase segregated from ammonia. [Preview Abstract] |
Wednesday, March 23, 2011 12:51PM - 1:03PM |
Q31.00007: Atomic structure and elastic properties at high pressure of aluminum oxynitride in cubic phase I.G. Batyrev, J.W. McCauley, B.M. Rice, G.A. Gazonas, A.R. Oganov The atomic structure and elastic properties of aluminum oxynitride spinel (AlON) at high pressure (up to 40 GPa) have been calculated from first principles. We have assumed an ``ideal'' stoichiometry of cubic AlON with 35.7 mole {\%} AlN using the constant anion model. The elastic constants were calculated from independent strains that were applied to a unit cell, parameterizing the total energy as a function of the strain and from a stress-strain relationship. At ambient conditions a clustered distribution of N atoms has $\sim $ 1 eV per 55 atoms higher total energy than for a random distribution and slightly, but systematically lower elastic constants. The pressure dependence of C$_{11}$, C$_{12}$ and C$_{44}$ for random and cluster distributions of N atoms was calculated in the range of 0-40 GPa by performing six finite distortions of the lattice and deriving the elastic constants from the strain-stress relationship. The calculated values of dC$_{11}$/dP are in the range of 4.0-6.2 and for dC$_{44}$/dP $\sim $0.8-1.5. The estimates are in reasonable agreement with experimental measurements of polycrystalline AlON. The minimum energy structure of AlON was found using the evolutionary algorithm USPEX (Oganov {\&} Glass, 2006) [Preview Abstract] |
Wednesday, March 23, 2011 1:03PM - 1:15PM |
Q31.00008: In Situ Neutron and Synchrotron X-ray Diffraction Studies of Jarosite at High-Temperature High-Pressure Conditions H. Xu, Y. Zhao, D. Hickmott, J. Zhang, S. Vogel, L. Daemen, M. Hartl Jarosite (KFe$_{3}$(SO$_{4})_{2}$(OH)$_{6})$ occurs in acid mine drainage and epithermal environments and hot springs associated with volcanic activity. Jarosite is also of industrial interest as an iron-impurity extractor from zinc sulfide ores. In 2004, jarosite was detected by the Mars Exploration Rover M\"{o}ssbauer spectrometer, which has been interpreted as a strong evidence for the existence of water (and possibly life) on ancient Mars. This discovery has spurred considerable interests in stability and structural behavior of jarosite and related phases at various temperature, pressure, and aqueous conditions. In this work, we have investigated the crystal structure and phase stability of jarosite at temperatures up to 900 K and/or pressures up to 9 GPa using \textit{in situ} neutron and synchrotron X-ray diffraction. To avoid the large incoherent scattering of neutrons by hydrogen, a deuterated sample was synthesized and characterized. Rietveld analysis of the obtained diffraction data allowed determination of unit-cell parameters, atomic positions and atomic displacement parameters as a function of temperature and pressure. In addition, the coefficients of thermal expansion, bulk moduli and pressure-temperature stability regions of jarosite were determined. [Preview Abstract] |
Wednesday, March 23, 2011 1:15PM - 1:27PM |
Q31.00009: Testing the minimum thermal conductivity model for amorphous polymers using high pressure Wen-Pin Hsieh, Mark Losego, Paul Braun, Sergei Shenogin, Pawel Keblinski, David Cahill Pressure dependence of thermal conductivity provides a critical test of the validity of the model of the minimum thermal conductivity for describing heat transport by molecular vibrations of an amorphous polymer. We measure the pressure dependence of the thermal conductivity of poly(methyl methacrylate) (PMMA) brushes grafted from SiC substrates using a combination of time-domain thermoreflectance and SiC anvil cell techniques. We also determine the pressure dependence of the thermal conductivity from a computational model of amorphous polystyrene. In both cases, thermal conductivity as a function of pressure is accurately predicted by the minimum thermal conductivity model via the pressure dependence of the elastic constants and density. [Preview Abstract] |
Wednesday, March 23, 2011 1:27PM - 1:39PM |
Q31.00010: The Influence of Crystal Structure on the Thermal Expansion Behavior of GeZn$_{2}$O$_{4}$ Michael Crawford, R.L. Harlow, W.E. Guise, R.A. Fisher, W. Woerner, J.B. Parise, Q. Huang, J.W. Lynn, R. Stevens, B. Woodfield, J. Boerio-Goates, J. Lashley, O. Gourdon, A. Huq, J. Hormadaly, P.L. Lee, Y. Zhang GeZn$_{2}$O$_{4}$ synthesized at ambient pressure adopts the rhombohedral phenacite crystal structure, whereas cubic or tetragonal inverse spinel phases are formed at high pressures. We have measured the thermal expansion for all three forms of GeZn$_{2}$O$_{4}$ at temperatures from 10 K to 400 K (or higher) using synchrotron x-ray powder diffraction. The phenacite form exhibits negative thermal expansion below 300 K, changing to positive thermal expansion above that temperature. In contrast to this behavior, the cubic and tetragonal inverse spinel phases exhibit positive thermal expansion below room temperature. Characterization of these materials using x-ray and neutron diffraction, as well as heat capacity and Raman spectroscopy, will be described. Possible structural reasons for the different thermal expansion behaviors of the phenacite and spinel forms of GeZn$_{2}$O$_{4}$ will be discussed. [Preview Abstract] |
Wednesday, March 23, 2011 1:39PM - 1:51PM |
Q31.00011: First-principles calculation of Ca2RuO4 at high pressure Nobumi Miyawaki, Tatsuya Shishidou, Tamio Oguchi It has been observed that the layered perovskite antiferromagnetic insulator Ca$_2$RuO$_4$ reveals a phase transition into a ferromagnetic metal at 0.5GPa [1]. This insulator-metal transition is accompanied by a structural change with tilt and rotation of RuO$_6$ octahedron within the space group $Pbca$. Above about 9GPa, another transition from the ferromagnetic to superconducting phase has been recently reported [2]. The transition includes a structure change from $Pbca$ to $Bbcm$. In this study, a first-principles calculation is performed to study the electronic structure of Ca$_2$RuO$_4$, especially focusing on the changes of Ru 4$d$ states, with pressure. As the pressure is increased, calculated ferromagnetic spin moment of Ru is gradually decreased in $Pbca$ owing to the widening of Ru 4$d$ band. It is interesting that a ferromagnetic solution still exists in $Bbcm$. Similar structural changes (the tilt and rotation of RuO$_6$ octahedron) take place in Ca$_{2-x}$Sr$_x$RuO$_4$, where orbital hybridization with spin-orbit coupling (SOC) is crucial [3]. We also investigated effects of SOC, with the result that those appear even in the electronic structure of Ca$_2$RuO$_4$. Calculation results optimizing the structure will be also discussed. [1] F. Nakamura, et al., Phys. Rev. B {\bf 65}, 220402(R) (2002). [2] P. L. Alireza, $et$ $al$.: J. Phys.: Condens. Matter {\bf 22}, 052202 (2010). [3] T. Oguchi, J. Phys. Soc. Jpn. {\bf 78}, 044702 (2009). [Preview Abstract] |
Wednesday, March 23, 2011 1:51PM - 2:03PM |
Q31.00012: Effect of high pressure on transport and structural properties of topological insulator Bi$_2$Se$_3$ J.J. Hamlin, J.R. Jeffries, N.P. Butch, P. Syers, D. A. Zocco, S.T. Weir, Y.K. Vohra, J. Paglione, M.B. Maple We report a series of electrical resistivity, magnetotransport, and xray diffraction measurements on the topological insulator Bi$_2$Se$_3$ under pressures as high as 34 GPa. The results demonstrate that applied pressure can be used to controllably tune the transport properties without chemical substitution. [Preview Abstract] |
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