Phase Transition in a Strongly Nonideal Deuterium Plasma Generated by Quasi-Isentropical Compression at Megabar Pressures

Фортов, В. Е.; Ilkaev, R.; Аринин, В. А.; Burtzev, V. V.; Golubev, Valery A; Iosilevskiy, Igor; Khrustalev, V. V.; Михайлов, А. Л.; Mochalov, M. A.; Ternovoǐ, V. Ya.; Zhernokletov, M. V.

doi:10.1103/physrevlett.99.185001

Cited by 204 publications

(167 citation statements)

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“…Their measured conductivity is consistent with DC values calculated for liquid-atomic metallic hydrogen by Morales et al (2); however, they do not observe a discontinuity, a property of the PPT. Fortov et al (12) also used reverberating shock waves to compress deuterium and report a large-density step at P ∼ 150 GPa and T ∼ 4,000 K. However, in this challenging experiment, their data are sparse, conductivity seems to be measured on another sample, and temperature and pressure are calculated, and therefore, this does not provide strong evidence of the PPT.…”

Section: Morales Et Al Predict Thementioning

confidence: 99%

The insulator-metal transition in hydrogen

Silvera

2010

Proc. Natl. Acad. Sci. U.S.A.

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I n their pioneering work over 75 years ago, Wigner and Huntington (1) predicted that solid molecular hydrogen would dissociate and become an atomic metal when pressurized to 25 GPa (25 GPa = 0.25 megabar) at a temperature T = 0 K. Subsequently, one of the great challenges of condensed matter physics in the past and present century has been to achieve metallization of hydrogen. Theory and experiment have worked hand in hand. Hydrogen is conceptually the simplest of all atoms, with a single proton and electron, doubled in the molecule, yet it is extremely challenging to theorists. This is mainly because of the light mass, resulting in large zero-point motion (i.e., motion of the nuclei of a many-body solid at 0 K). To achieve the most accurate theoretical results, a full quantum mechanical analysis is required at all densities and conditions.Following Wigner and Huntington (1), predictions of the metallization pressure (P) have ranged as high as 20 megabars and currently, are in the range of 4-6 megabars. This has been somewhat guided by experiment: the highest static pressures achieved with diamond anvil cells have been ∼3.5 megabar, with hydrogen remaining an insulating molecular solid. Further predictions for metallic hydrogen are that it would be metastable (i.e., remain in the metallic state when pressure is released), may be a room temperature superconductor, and may even be a liquid at 0 K when compressed to the atomic metallic state. To test these predictions, a statically compressed sample at modest temperatures will be required.A second path to metallization of hydrogen is at high temperature and pressure in the liquid phase. This region is called hot-dense matter and is of particular interest to planetary scientists; these are the conditions found in the giant outer planets and exoplanets where the dense matter can exist as a plasma. A plasma is a fluid with ionized atoms or molecules. In a fluorescent lamp, a low-density, lowtemperature gas of atoms is ionized by an applied electric field. At high enough temperatures and pressures in a gas or liquid, a plasma can be formed because a certain portion of the particles are thermally ionized and the condensed matter system can electrically conduct. The article by Morales et al. (2) in PNAS predicts a first-order phase transition to a metallic phase of liquid atomic hydrogen at high pressure and temperature. This is the so-called plasma-phase transition (PPT). A possible phase diagram of hydrogen is shown in Fig. 1.Theoretical studies have various degrees of sophistication, and because predictions of properties of hydrogen have had a number of conflicting results, it is useful to classify these. Most modern studies of hydrogen use Monte Carlo or moleculardynamics simulations requiring substantial computing resources. Here, a large number of particles are allowed to collide or interact with each other until they achieve an equilibrium phase. The least demanding approach is to use effective pair potentials for each density, but these do not accurately handle...

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Section: Morales Et Al Predict Thementioning

confidence: 99%

The insulator-metal transition in hydrogen

Silvera

2010

Proc. Natl. Acad. Sci. U.S.A.

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“…Until few years ago, all the few experimental observations [25][26][27] located the insulator to metal transition (IMT), which provides a lower bound for the molecular to atomic transition, at pressures of ∼ 140 GPa in the temperature range of 1500-3000 K. Concurring numerical simulations [28][29][30], using both DFT, with Perdew-BurkeErnzerhof (PBE) exchange-correlation functional [31], and QMC agreed with this value. In Ref.…”

mentioning

confidence: 59%

Acceleratingab initioMolecular Dynamics and Probing the Weak Dispersive Forces in Dense Liquid Hydrogen

Mazzola

Sorella

2017

Phys. Rev. Lett.

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We propose an ab-initio molecular dynamics method, capable to reduce dramatically the autocorrelation time required for the simulation of classical and quantum particles at finite temperature. The method is based on an efficient implementation of a first order Langevin dynamics modified by means of a suitable, position dependent acceleration matrix S. Here we apply this technique, within a Quantum Monte Carlo (QMC) based wavefunction approach and within the Born-Oppheneimer approximation, for determining the phase diagram of high-pressure Hydrogen with simulations much longer than the autocorrelation time. With the proposed method, we are able to equilibrate in few hundreds steps even close to the liquid-liquid phase transition (LLT). Within our approach we find that the LLT transition is consistent with recent density functionals predicting a much larger transition pressures when the long range dispersive forces are taken into account.One of the most important problems in ab-initio molecular dynamics (MD) is the coexistence of much different time scales underlying physical processes, even when computing equilibrium finite temperature properties. This has been a challenge for most ab-initio simulations in systems of biophysical interest, the most striking one being protein folding [1,2], where the microscopic time scale of molecular vibration is of the order of f s, while the macroscopic time scale of the folding exceeds the µs. Also in water system simulations, the weak Van der Waals (vdW) interactions and the related hydrogen bond imply very difficult equilibration properties at ambient conditions, so that the most accurate simulations are based on force field fitting forces. We will show here that, a computationally expensive ab-initio method for dense liquid hydrogen can be combined with a sampling technique capable to reduce drastically the autocorrelation times. This method has the potential, due to its simplicity, to be applied with success also to much more complex systems and other ab-initio techniques.At variance of all previous attempts[3-10], we propose that an optimal way to get rid of different time scales is based on the use of first order Langevin dynamics:where T is the temperature, f Ri = −∂ Ri V ( R) and V R is an energy potential of the classical coordinates R, e.g. atomic positions. For S ij = δ ij this is the conventional first order Langevin dynamics (CFOLD). Preconditioned Langevin equations, formally similar to Eq. 40, have been already introduced in several fields different from molecular dynamics, such as gauge field theories[11], statistics [12] and machine learning [13], with different definitions of the preconditioning matrix S. Instead, the main idea of this work is based on the simple solution of CFOLD for the harmonic potential V (R) = −K R, where K is the elastic matrix term. In this case one is able to show that the i) the autocorrelation time is independent of temperature τ −1 corr = K min , where K min (K max ) is the lowest (largest) non-zero eigenvalue of the elastic matrix...

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“…The gas pressure was controlled by a standard pressure gauge. The required pressure needed to obtain an initial density of 0.019 g/cm 3 was calculated based upon the initial temperature of the gas. For the performed tests, this resulted in an initial pressure of 120 ± 5 atm.…”

Section: Cylindrical Designmentioning

confidence: 99%

“…The densities attained ranged from 1.3 to 2.3 g/cm 3 with a compression ratio 0 δ = ρ ρ from 70 to 120. The absence in the data of a significant jump in the density of helium under the investigated area of pressures and densities implies there is no underlying phase transition.…”

Section: X V P T V P →mentioning

confidence: 99%

“…Compression in this manner approaches an isentropic process, for the change in entropy is smaller for the first and the subsequent shock waves. Earlier research using cylindrical steel chambers filled with gaseous deuterium demonstrated this quasi-isentropic compression process [3]. These chambers are able to hold the gas at high pressure longer than what one can obtain from a single shock wave.…”

Section: Introductionmentioning

confidence: 97%

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Quasi-isentropic compression of gaseous helium in pressure range from 130 to 460 GPa

Zhernokletov¹,

Аринин²,

Buzin³

et al. 2012

AIP Conference Proceedings

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Abstract.Here we present the results for experiments of gaseous helium with an initial density of 0.019 g/cm 3 cylindrically compressed. The cylindrical compression technique transforms shock compression to quasi-isentropic compressions. The resulting pressures attained were from 130 to 460 GPa with compressed densities of 1.3 to 2.3 g/cm 3 for a compression ratio ( 0 δ = ρ ρ ) from 70 to 115.The density of the gas was determined from X-ray radiography based on the boundary location of the steel liners, which compressed the gas. The pressures Gas density was determined by the X-ray radiography method basing on location of boundaries of the steel shells, which compressed gas. Pressures were based upon gas-dynamic calculations.

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Phase Transition in a Strongly Nonideal Deuterium Plasma Generated by Quasi-Isentropical Compression at Megabar Pressures

Cited by 204 publications

References 20 publications

The insulator-metal transition in hydrogen

The insulator-metal transition in hydrogen

Acceleratingab initioMolecular Dynamics and Probing the Weak Dispersive Forces in Dense Liquid Hydrogen

Quasi-isentropic compression of gaseous helium in pressure range from 130 to 460 GPa

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