Molecular to Atomic Phase Transition in Hydrogen under High Pressure

McMinis, Jeremy; Clay, Raymond C.; Lee, Donghwa; Morales, Miguel A.

doi:10.1103/physrevlett.114.105305

Cited by 150 publications

(169 citation statements)

References 49 publications

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“…This process occurs over a range of pressures of roughly 200GPa, pointing to the progressive character of the metallization process in these molecular crystals. A possible different mechanism would be an abrupt metallization driven by a structural phase transition to a monoatomic phase as proposed by ground state QMC calculations [30,31], a mechanism that remains out of the reach of our simulations. Figure 10 reports the density dependence of the static conductivities for both C2c and Cmca12 structures.…”

Section: Electronic Propertiesmentioning

confidence: 88%

“…We performed simulations of solid hydrogen at finite temperature along two isotherms at T=200 K and T=414 K. At T=200 K, for pressures between 250-500 GPa, we considered C2c, Cmca12 and Cmca4 structures using PIMD and C2c and Cmca12 structures for CEIMC ( Cmca4 is excluded by static QMC calculation [30,31]). At T=414 K we considered only Pc48 in a range of 250-350 GPa, since both DFT and QMC found this structure stable at higher temperatures [23,32,40].…”

Section: Methodsmentioning

confidence: 99%

“…These calculations could investigate both the influence of the exchange-correlation approximation and the nuclear quantum effects on the dynamical stability of the considered structures. On the other hand, static lattice energies were computed by the more reliable Quantum Monte Carlo methods [30][31][32][33]. However in these studies the treatment of finite temperature and nuclear quantum effects still relied on perturbation theory and the PBE-DFT functional.…”

Section: Introductionmentioning

confidence: 99%

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Coupled electron-ion Monte Carlo simulation of hydrogen molecular crystals

Rillo

Morales

Ceperley

et al. 2017

The Journal of Chemical Physics

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We performed simulations for solid molecular hydrogen at high pressures (250GPa≤P≤500GPa) along two isotherms at T=200 K (phases III and VI) and at T=414 K (phase IV). At T=200K we considered likely candidates for phase III, the C2c and Cmca12 structures, while at T=414K in phase IV we studied the Pc48 structure. We employed both Coupled Electron-Ion Monte Carlo (CEIMC) and Path Integral Molecular Dynamics (PIMD) based on Density Functional Theory (DFT) using the vdW-DF approximation. The comparison between the two methods allows us to address the question of the accuracy of the xc approximation of DFT for thermal and quantum protons without recurring to perturbation theories. In general, we find that atomic and molecular fluctuations in PIMD are larger than in CEIMC which suggests that the potential energy surface from vdW-DF is less structured than the one from Quantum Monte Carlo. We find qualitatively different behaviors for systems prepared in the C2c structure for increasing pressure. Within PIMD the C2c structure is dynamically partially stable for P≤250GPa only: it retains the symmetry of the molecular centers but not the molecular orientation; at intermediate pressures it develops layered structures like Pbcn or Ibam and transforms to the metallic Cmca-4 structure at P≥450GPa. Instead, within CEIMC, the C2c structure is found to be dynamically stable at least up to 450GPa; at increasing pressure the molecular bond length increases and the nuclear correlation decreases. For the other two structures the two methods are in qualitative agreement although quantitative differences remain. We discuss various structural properties and the electrical conductivity. We find these structures become conducting around 350GPa but the metallic Drude-like behavior is reached only at around 500GPa, consistent with recent experimental claims.

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Section: Electronic Propertiesmentioning

confidence: 88%

Section: Methodsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Coupled electron-ion Monte Carlo simulation of hydrogen molecular crystals

Rillo

Morales

Ceperley

et al. 2017

The Journal of Chemical Physics

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“…Modern calculations yield a transition pressure of 400-500 GPa for MH (see Refs. [12,13]). After briefly reviewing recent and historical developments we present an innovative method that allows measurement of transmittance (Tr) and reflectance (R) of hydrogen statically pressurized and heated to a metallic phase, reported recently [14].…”

Section: Introductionmentioning

confidence: 99%

Evidence of a first-order phase transition to metallic hydrogen

Zaghoo¹,

Salamat²,

Silvera³

2016

Phys. Rev. B

138

166

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“…In pure hydrogen, one can at least quantify the impact of density functional errors on the phase diagram, both because of explicit benchmarking studies, and because the phase diagram has been computed by many different groups and methods, ranging from slews of different functionals to highly accurate QMC methods. Various studies have found that the pure hydrogen phase diagram is extremely sensitive to the choice of exchange correlation functional, primarily because of the presence of multiple molecular disassociation and metallization phase transitions and crossovers [14][15][16][17] . In contrast, little is known of the impact that density functionals errors have on the demixing temperature in dense H+He mixtures.…”

Section: Introductionmentioning

confidence: 99%

Benchmarking density functionals for hydrogen-helium mixtures with quantum Monte Carlo: Energetics, pressures, and forces

et al. 2016

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An accurate understanding of the phase diagram of dense hydrogen and helium mixtures is a crucial component in the construction of accurate models of Jupiter, Saturn, and Jovian extrasolar planets. Though DFT based first principles methods have the potential to provide the accuracy and computational efficiency required for this task, recent benchmarking in hydrogen has shown that achieving this accuracy requires a judicious choice of functional, and a quantification of the errors introduced. In this work, we present a quantum Monte Carlo based benchmarking study of a wide range of density functionals for use in hydrogen-helium mixtures at thermodynamic conditions relevant for Jovian planets. Not only do we continue our program of benchmarking energetics and pressures, but we deploy QMC based force estimators and use them to gain insights into how well the local liquid structure is captured by different density functionals. We find that TPSS, BLYP and vdW-DF are the most accurate functionals by most metrics, and that the enthalpy, energy, and pressure errors are very well behaved as a function of helium concentration. Beyond this, we highlight and analyze the major error trends and relative differences exhibited by the major classes of functionals, and estimate the magnitudes of these effects when possible.

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Molecular to Atomic Phase Transition in Hydrogen under High Pressure

Cited by 150 publications

References 49 publications

Coupled electron-ion Monte Carlo simulation of hydrogen molecular crystals

Coupled electron-ion Monte Carlo simulation of hydrogen molecular crystals

Evidence of a first-order phase transition to metallic hydrogen

Benchmarking density functionals for hydrogen-helium mixtures with quantum Monte Carlo: Energetics, pressures, and forces

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