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Ping Zhang - One of the best experts on this subject based on the ideXlab platform.
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First-principles calculation of principal Hugoniot and K-shell X-ray absorption spectra for warm dense KCl
Physics of Plasmas, 2015Co-Authors: Shijun Zhao, Shen Zhang, Wei Kang, Ping ZhangAbstract:Principal Hugoniot and K-shell X-ray absorption spectra of warm dense KCl are calculated using the first-principles molecular dynamics (FPMD) method. Evolution of electronic structures as well as the influence of the approximate description of ionization on Pressure (caused by the underestimation of the energy gap between conduction bands and valence bands) in the first-principles method are illustrated by the calculation. It is shown that approximate description of ionization in FPMD has small influence on Hugoniot Pressure due to mutual compensation of electronic kinetic Pressure and virial Pressure. The calculation of X-ray absorption spectra shows that the band gap of KCl persists after the Pressure ionization of the 3p electrons of Cl and K taking place at lower energy, which provides a detailed understanding to the evolution of electronic structures of warm dense matter.
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Quantum molecular dynamic simulations of warm dense carbon monoxide.
The Journal of chemical physics, 2011Co-Authors: Yujuan Zhang, Cong Wang, Ping ZhangAbstract:Using quantum molecular dynamic simulations, we have studied the thermophysical properties of warm dense carbon monoxide under extreme conditions. The principal Hugoniot Pressure up to 286 GPa, which is derived from the equation of state, is calculated and compared with available experimental and theoretical data. The chemical decomposition of carbon monoxide has been predicted at 8 GPa by means of pair correlation function and the charge density distribution. Based on Kubo-Greenwood formula, the dc electrical conductivity and the optical reflectivity are determined, and the nonmetal-metal transition for shock compressed carbon monoxide is observed around 40 GPa.
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Equation of state for shock-compressed porous molybdenum from first-principles mean-field potential calculations
arXiv: Materials Science, 2007Co-Authors: Qili Zhang, Ping Zhang, Gongmu Zhang, Haifeng LiuAbstract:The Hugoniot curves for shock-compressed molybdenum with initial porosities of 1.0, 1.26, 1.83, and 2.31 are theoretically investigated. The method of calculations combines the first-principles treatment for zero- and finite-temperature electronic contribution and the mean-field-potential approach for the ion-thermal contribution to the total free energy. Our calculated results reproduce the Hugoniot properties of porous molybdenum quite well. At low porosity, in particular, the calculations show a complete agreement with the experimental measurements over the full range of data. For the two large porosity values of 1.83 and 2.31, our results are well in accord with the experimental data points up to the particle velocity of 3.5 km/s, and tend to overestimate the shock-wave velocity and Hugoniot Pressure when further increasing the particle velocity. In addition, the temperature along the principal Hugoniot is also extensively investigated for porous molybdenum.
R. B. Barreiro - One of the best experts on this subject based on the ideXlab platform.
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Planck intermediate results - X. Physics of the hot gas in the Coma cluster
Astronomy & Astrophysics, 2013Co-Authors: P. A. R. Ade, N. Aghanim, M. Arnaud, M. Ashdown, F. Atrio-barandela, J. Aumont, C. Baccigalupi, A. Balbi, A. J. Banday, R. B. BarreiroAbstract:We present an analysis of Planck satellite data on the Coma Cluster observed via the Sunyaev-Zeldovich effect. Thanks to its great sensitivity, Planck is able, for the first time, to detect SZ emission up to r ≈ 3× R500. We test previously proposed spherically symmetric models for the Pressure distribution in clusters against the azimuthally averaged data. In particular, we find that the Arnaud et al. (2 010) “universal” Pressure profile does not fit Coma, and that their Pressure profile for me rging systems provides a reasonable fit to the data only at r R500 than the mean Pressure profile predicted by the simulations used to constrain the models. The Planck image shows significant local steepening of the y profile in two regions about half a degree to the west and to the south-east of the cluster centr e. These features are consistent with the presence of shock fronts at these radii, and indeed the western feature was previously noticed in the ROSAT PSPC mosaic as well as in the radio. Using Planck y profiles extracted from corresponding sectors we find Pressure jumps of 4.9 +0.4 −0.2 and 5.0 +1.3 −0.1 in the west and south-east, respectively. Assuming Rankine-Hugoniot Pressure jump conditions, we deduce that the shock waves should propagate with Mach number Mw = 2.03 +0.09 −0.04 and Mse = 2.05 +0.25 −0.02 in the west and south-east, respectively. Finally, we find that the y and radio-synchrotron signals are quasi-linearly correla ted on Mpc scales, with small intrinsic scatter. This implies either that the energy density of cosm ic-ray electrons is relatively constant throughout the clu ster, or that the magnetic fields fall off much more slowly with radius than previously thought.
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Planck intermediate results
Astronomy and Astrophysics - A&A, 2013Co-Authors: P. A. R. Ade, N. Aghanim, M. Arnaud, M. Ashdown, F. Atrio-barandela, J. Aumont, C. Baccigalupi, A. Balbi, A. J. Banday, R. B. BarreiroAbstract:We present an analysis of Planck satellite data on the Coma cluster observed via the Sunyaev-Zeldovich effect. Thanks to its great sensitivity, Planck is able, for the first time, to detect SZ emission up to r ≈ 3 × R500. We test previously proposed spherically symmetric models for the Pressure distribution in clusters against the azimuthally averaged data. In particular, we find that the Arnaud et al. (2010, A&A, 517, A92) “universal” Pressure profile does not fit Coma, and that their Pressure profile for merging systems provides a reasonable fit to the data only at r R500 than the mean Pressure profile predicted by the simulations used to constrain the models. The Planck image shows significant local steepening of the y profile in two regions about half a degree to the west and to the south-east of the cluster centre. These features are consistent with the presence of shock fronts at these radii, and indeed the western feature was previously noticed in the ROSAT PSPC mosaic as well as in the radio. Using Plancky profiles extracted from corresponding sectors we find Pressure jumps of 4.9-0.2+0.4 and 5.0-0.1+1.3 in the west and south-east, respectively. Assuming Rankine-Hugoniot Pressure jump conditions, we deduce that the shock waves should propagate with Mach number Mw = 2.03-0.04+0.09 and Mse = 2.05-0.02+0.25 in the west and south-east, respectively. Finally, we find that the y and radio-synchrotron signals are quasi-linearly correlated on Mpc scales, with small intrinsic scatter. This implies either that the energy density of cosmic-ray electrons is relatively constant throughout the cluster, or that the magnetic fields fall off much more slowly with radius than previously thought.
Lee A. Collins - One of the best experts on this subject based on the ideXlab platform.
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Properties of warm dense polystyrene plasmas along the principal Hugoniot.
Physical review. E Statistical nonlinear and soft matter physics, 2014Co-Authors: T. R. Boehly, Lee A. CollinsAbstract:Polystyrene (CH) is often chosen as the ablator material for inertial confinement fusion (ICF) targets. Its static, dynamical, and optical properties in warm, dense conditions (due to shock compression) are important for ICF designs. Using the first-principles quantum molecular dynamics (QMD) method, we have investigated the equation of state (EOS) and optical reflectivity of shock-compressed CH up to an unprecedentedly high Pressure of 62 Mbar along the principal Hugoniot. The QMD results are compared with existing experimental measurements as well as the SESAME EOS model. Although the Hugoniot Pressure and/or temperature from QMD calculations agrees with experiments and the SESAME EOS model at low Pressures below 10 Mbar, we have identified for the first time a stiffer behavior of shocked CH at higher Pressures (>10 Mbar). Such a stiffer behavior of warm, dense CH can affect the ablation Pressure (shock strength), shock coalescence dynamics, and nonuniformity growth in ICF implosions. In addition, we corrected the mistake made in literature for calculating the reflectivity of shocked CH and obtained good agreements with experimental measurements, which should lend credence to future opacity calculations in a first-principles fashion.
Alessandro Curioni - One of the best experts on this subject based on the ideXlab platform.
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ab initio simulation of the equation of state and kinetics of shocked water
Journal of Chemical Physics, 2009Co-Authors: Nir Goldman, Christopher J Mundy, Laurence E. Fried, Evan J Reed, Alessandro CurioniAbstract:We report herein first principles simulations of water under shock loading and the chemical reactivity under these hot, compressed conditions. Using a recently developed simulation technique for shock compression, we observe that water achieves chemical equilibrium in less than 2 ps for all shock conditions studied. We make comparison to the experimental results for the Hugoniot Pressure and density final states. Our simulations show that decomposition occurs through the reversible reaction H2O↔H++OH−, in agreement with experiment. Near the approximate intersection of the Hugoniot and the Neptune isentrope, we observe high concentrations of charged species that contribute electronic states near the band gap.
Zhong-li Liu - One of the best experts on this subject based on the ideXlab platform.
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Phasego: A toolkit for automatic calculation and plot of phase diagram
Computer Physics Communications, 2015Co-Authors: Zhong-li LiuAbstract:a b s t r a c t The Phasego package extracts the Helmholtz free energy from the phonon density of states obtained by the first-principles calculations. With the help of equation of states fitting, it reduces the Gibbs free energy as a function of Pressure/temperature at fixed temperature/Pressure. Based on the quasi-harmonic approximation (QHA), it calculates the possible phase boundaries among all the structures of interest and finally plots the phase diagram automatically. For the single phase analysis, Phasego can numerically derive many properties, such as the thermal expansion coefficients, the bulk moduli, the heat capacities, the thermal Pressures, the Hugoniot Pressure–volume–temperature relations, the Gruneisen parameters, and the Debye temperatures. In order to check its ability of phase transition analysis, I present here two examples: semiconductor GaN and metallic Fe. In the case of GaN, Phasego automatically determined and plotted the phase boundaries among the provided zinc blende (ZB), wurtzite (WZ) and rocksalt (RS) structures. In the case of Fe, the results indicate that at high temperature the electronic thermal excitation free energy corrections considerably alter the phase boundaries among the body-centered cubic (bcc), face-centered cubic (fcc) and hexagonal close-packed (hcp) structures.
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Phasego 2.0: Counting full anharmonic effects from high-temperature phonon density of states
Computer Physics Communications, 2015Co-Authors: Zhong-li LiuAbstract:Abstract In this paper, we present a revised version of Phasego 1.0 toolkit. The automatic anharmonic effects analysis functionality is added to perform the full anharmonic corrections for the quasi-harmonic approximation (QHA) results. The anharmonic free energies are extracted from the high-temperature phonon density of states (DOS), and then the phase boundaries and other properties can be automatically corrected by taking into account full anharmonic effects. New version program summary Program title: Phasego2 Catalogue identifier: AEVQ_v2_0 Program summary URL: http://cpc.cs.qub.ac.uk/summaries/AEVQ_v2_0.html Program obtainable from: CPC Program Library, Queen’s University, Belfast, N. Ireland Licensing provisions: GNU General Public License, version 3 No. of lines in distributed program, including test data, etc.: 5867093 No. of bytes in distributed program, including test data, etc.: 56696690 Distribution format: tar.gz Programming language: Python (versions 2.4 and later). Computer: Any computer that can run Python (versions 2.4 and later). Operating system: Any operating system that can run Python. RAM: 50 M bytes Classification: 7.8. Catalogue identifier of previous version: AEVQ_v1_0 Journal reference of previous version: Comput. Phys. Comm. 191 (2015) 150 External routines: Numpy [1], Scipy [2], Matplotlib [3] Does the new version supersede the previous version?: Yes Nature of problem: The anharmonic lattice vibrations have more and more contributions to Gibbs free energy when temperature is beyond Debye temperature and goes up to melting temperature. The quasi-harmonic approximation (QHA) only includes part of the anharmonic effects due to the volume variation of frequency. At high temperature, the neglect of phonon–phonon interactions in the QHA will introduce errors and even arrive at wrong conclusions. However, the calculation of the anharmonic free energy from the phonon–phonon interactions is very complicated to perform. Solution method: The contribution of phonon–phonon interactions to free energy can be naturally extracted from the high-temperature phonon density of states (DOS). The extraction and inclusion of anharmonic free energy are simplified and automated in the updated version. The thermal properties of materials are then corrected by including full anharmonic effects with respective to the QHA results. Reasons for new version: We have improved the package considerably to include full anharmonic contributions of phonon–phonon interactions. The calculations of thermal properties of materials are automated and easy to implement after anharmonic corrections. Summary of revisions: • The anharmonic free energy extraction functionality is added. Now the Gibbs free energy can include full anharmonic effects. • The thermal expansion coefficients are deduced by taking into account full anharmonic contributions. • The bulk moduli, the heat capacities, the thermal Pressures can include and reflect the contributions of phonon–phonon interactions. • The Hugoniot Pressure–volume–temperature relations, the Gruneisen parameters, and the Debye temperatures are corrected by anharmonic effects. • The Polynomial curve fitting of Helmholtz free energy is added. • The unit of Gibbs free energy in the output files is changed. • A number of bugs have been corrected. Restrictions: The restrictions are from the high-temperature phonon DOS calculations. The smaller interval of temperatures at which the phonon DOS are calculated will yield more accurate results. The accuracy of the previously calculated phonon DOS also affect that of the final results. Unusual features: The Gibbs free energy of phonon–phonon interactions are automatically extracted from the high-temperature phonon DOS. The anharmonic effects of all the thermal properties are automatically corrected. Additional comments: The new version of this package can treat the high-temperature phonon density of states data from many methods, including the molecular dynamics (MD) simulations [4], the self-consistent ab initio lattice dynamics (SCAILD) calculations [5], or other simulation methods. The distribution file for this program is over 56 Mbytes and therefore is not delivered directly when download or Email is requested. Instead a html file giving details of how the program can be obtained is sent. Running time: The examples provided in the distribution take less than 5 minute to run. References: [1] www.numpy.org . [2] www.scipy.org . [3] www.matplotlib.org . [4] O. Hellman, I. A. Abrikosov, and S. I. Simak, Phys. Rev. B, 84 (2011) 180301. [5] P. Souvatzis, O. Eriksson, M. I. Katsnelson, S. P. Rudin, Phys. Rev. Lett., 100 (2008) 095901.