Large-scale quantum mechanical simulations of high-Z metals

Yang, Lihui; Hood, Randolph Q.; Pask, John E.; Klepeis, John E.

doi:10.1007/s10820-007-9053-1

Cited by 10 publications

(6 citation statements)

References 35 publications

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“…55,56 We have used Born-Oppenheimer QMD in which the low lying single-particle electronic eigenstates are computed by solving the selfconsistent DFT Kohn-Sham equations 2 within the framework of Mermin's finite temperature density functional theory. 57 To accomplish this we used a preconditioned conjugate gradient method 3,58,59 to fully relax the electronic wavefunctions at each time step. An efficient fast Fourier transform algorithm was used for the conversion of the wave functions between real and reciprocal spaces.…”

Section: Qmd Results and Discussionmentioning

confidence: 99%

“…An efficient fast Fourier transform algorithm was used for the conversion of the wave functions between real and reciprocal spaces. 59 The electronic eigenstates were thermally occupied using the FermiDirac distribution function at a temperature T electron equivalent to the ion temperature. The use of a pseudopotential along with a plane-wave basis allowed us to accurately calculate the forces acting on the ions.…”

Section: Qmd Results and Discussionmentioning

confidence: 99%

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Quantum molecular dynamics simulations of uranium at high pressure and temperature

2008

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Constant-volume quantum molecular dynamics (QMD) simulations of uranium (U) have been carried out over a range of pressures and temperatures that span the experimentally observed solid orthorhombic α-U, body-centered cubic (bcc), and liquid phases, using an ab initio plane-wave pseudopotential method within the generalized gradient approximation of density functional theory.A robust U pseudopotential has been constructed for these simulations that treats the 14 valence and outer-core electrons per atom necessary to calculate accurate structural and thermodynamic properties up to 100 GPa. Its validity has been checked by comparing low-temperature results with experimental data and all-electron full-potential linear-muffin-tin-orbital calculations of several different uranium solid structures. Calculated QMD energies and pressures for the equation of state of uranium in the solid and liquid phases are given, along with results for the Grüneisen parameter and the specific heat. We also present results for the radial distribution function, bondangle distribution function, electronic density of states, and liquid diffusion coefficient, as well as evidence for short-range order in the liquid.

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Section: Qmd Results and Discussionmentioning

confidence: 99%

Section: Qmd Results and Discussionmentioning

confidence: 99%

Quantum molecular dynamics simulations of uranium at high pressure and temperature

2008

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“…The pwONCV calculations at low temperature (< 1.3 × 10 5 K) are similar to those using pwPAW. We applied a preconditioned conjugate gradient method 84 to fully relax the electronic wavefunctions at each time step. An efficient fast Fourier transform (FFT) algorithm was used for the conversion of the wave functions between real and reciprocal spaces.…”

Section: Dft-md With Optimized Norm-conserving Vanderbilt Pseudopomentioning

confidence: 99%

Equation of state of boron nitride combining computation, modeling, and experiment

et al. 2019

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The equation of state (EOS) of materials at warm dense conditions poses significant challenges to both theory and experiment. We report a combined computational, modeling, and experimental investigation leveraging new theoretical and experimental capabilities to investigate warm-dense boron nitride (BN). The simulation methodologies include path integral Monte Carlo (PIMC), several density functional theory (DFT) molecular dynamics methods [plane-wave pseudopotential, Fermi operator expansion (FOE), and spectral quadrature (SQ)], activity expansion (ACTEX), and all-electron Green's function Korringa-Kohn-Rostoker (MECCA), and compute the pressure and internal energy of BN over a broad range of densities and temperatures. Our experiments were conducted at the Omega laser facility and the Hugoniot response of BN to unprecedented pressures (1200-2650 GPa). The EOSs computed using different methods cross validate one another in the warm-dense matter regime, and the experimental Hugoniot data are in good agreement with our theoretical predictions. By comparing the EOS results from different methods, we assess that the largest discrepancies between theoretical predictions are 4% in pressure and 3% in energy and occur at 10 6 K, slightly below the peak compression that corresponds to the K-shell ionization regime. At these conditions, we find remarkable consistency between the EOS from DFT calculations performed on different platforms and using different exchange-correlation functionals and those from PIMC using free-particle nodes. This provides strong evidence for the accuracy of both PIMC and DFT in the high-pressure, high-temperature regime. Moreover, the recently developed SQ and FOE methods produce EOS data that have significantly smaller statistical error bars than PIMC, and so represent significant advances for efficient computation at high temperatures. The shock Hugoniot predicted by PIMC, ACTEX, and MECCA shows a maximum compression ratio of 4.55±0.05 for an initial density of 2.26 g/cm 3 , higher than the Thomas-Fermi predictions by about 5%. In addition, we construct new tabular EOS models that are consistent with the first-principles simulations and the experimental data. Our findings clarify the ionic and electronic structure of BN over a broad range of temperatures and densities and quantify their roles in the EOS and properties of this material. The tabular models may be utilized for future simulations of laser-driven experiments that include BN as a candidate ablator material. (LLNL-JRNL-767019-DRAFT)

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“…For the isothermal QMD simulations, we have used a plane-wave pseudopotential method 3 [23,24,26] as implemented with optimized norm-conserving Vanderbilt (ONCV) pseudopotentials of Hamann [27,28]. A dual-projector ONCV scalar-relativistic pseudopotential for Zr was constructed using Perdew-Burke-Ernzerhof (PBE) gradient density functional [29] to treat 12 valence (4s 2 4p 6 4d 2 5s 2 ) electrons.…”

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confidence: 99%

Anharmonicity-induced first-order isostructural phase transition of zirconium under pressure

et al. 2018

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We have performed a detailed x-ray diffraction structural study of Zr under pressure and unambiguously identify the existence of a first-order isostructural bcc-to-bcc phase transition near 58 GPa. First-principles quantum molecular dynamics lattice dynamics calculations support the existence of this phase transition, in excellent agreement with experimental results, triggered by anharmonic effects. Our results highlight the potential ubiquity of anharmonically driven isostructural transitions within the periodic table under pressure and calls for follow-up experimental and theoretical studies.

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Large-scale quantum mechanical simulations of high-Z metals

Cited by 10 publications

References 35 publications

Quantum molecular dynamics simulations of uranium at high pressure and temperature

Quantum molecular dynamics simulations of uranium at high pressure and temperature

Equation of state of boron nitride combining computation, modeling, and experiment

Anharmonicity-induced first-order isostructural phase transition of zirconium under pressure

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