Hydrogen and its compounds under extreme pressure

Utyuzh, A. N.; Mikheyenkov, A. V.

doi:10.3367/ufne.2017.02.038077

Cited by 11 publications

(5 citation statements)

References 91 publications

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“…[26] While most theoretical works suggest that it is a first-order transition, [1][2][3][4][5][6][7][8][9][10] there is an uncertainty in the experimental verification. [26] While most theoretical works suggest that it is a first-order transition, [1][2][3][4][5][6][7][8][9][10] there is an uncertainty in the experimental verification.…”

Section: First-order Naturementioning

confidence: 99%

“…In general, the discontinuous behaviour of the phase transition in fluid hydrogen is still under consideration. [26] While most theoretical works suggest that it is a first-order transition, [1][2][3][4][5][6][7][8][9][10] there is an uncertainty in the experimental verification. A part of the experiments demonstrates the first-order features, [4,[27][28][29][30][31][32] and the others affirm only an abrupt increase of the conductivity.…”

Section: First-order Naturementioning

confidence: 99%

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Metastable molecular fluid hydrogen at high pressures

Norman

Saitov

Sartan

2019

Contributions to Plasma Physics

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Warm dense hydrogen is studied in the region of fluid-fluid phase transition within the framework of the density functional theory. We report a procedure of obtaining metastable states and calculate the equation of state. Metastable states are diagnosed by pair correlation functions and values of conductivity. We obtain a strong overlapping through the density of metastable and equilibrium branches of pressure isotherms. This indicates the plasma nature of the phase transition. KEYWORDS density functional theory, equation of state, metastable states, warm dense hydrogen 1We present a method for the calculation of molecular metastable states of warm dense hydrogen within the framework of the DFT. The metastable states are diagnosed by PCFs and values of conductivity. The existence of metastable states indicates that the phase transition is a first-order phase transition. Note the following results:1 The metastable states are obtained for 700 and 1000 K isotherms. The isotherms have a peculiar sloped form with a strong overlapping of equilibrium and metastable branches and a rather small difference of specific volumes between branches. The overlapping found corresponds to the prediction [17] for the plasma phase transition. 2 The small jump of the specific volume at the phase transition prevents us from resolving metastable states at higher temperatures. 3 The phase coexistence line on the specific volume-pressure plane looks like a long and very narrow tongue. In this case, the accuracy of calculations does not permit us to locate the critical point within the interval of several thousand Kelvin. 4 The transition is overturned by a sequence of van der Waals loops, when an increase in temperature leads to a decrease in pressure, at which point the transition occurs as opposed to the conventional picture. 5 The findings from this study present arguments, in addition to, [5,8,49] in favour of the plasma nature of the fluid-fluid phase transition in warm dense hydrogen.

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Section: First-order Naturementioning

confidence: 99%

Section: First-order Naturementioning

confidence: 99%

Metastable molecular fluid hydrogen at high pressures

Norman

Saitov

Sartan

2019

Contributions to Plasma Physics

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“…The behaviour of hydrogen under conditions of extreme compression (20-400 GPa) and high temperatures (500-5000 K) has been studied for quite a long time [1][2][3][4][5] but its theoretical description still poses many unresolved questions. [6][7][8] One of these problems is the transition of compressed hydrogen in both solid and fluid states into a conducting state (metallization of solid hydrogen was predicted a long time ago).…”

Section: Introductionmentioning

confidence: 99%

Exciton Nature of Plasma Phase Transition in Warm Dense Fluid Hydrogen: ROKS Simulation**

Fedorov

Stegaĭlov

2022

ChemPhysChem

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The transition of warm dense fluid hydrogen from an insulator to a conducting state at pressures of about 20–400 GPa and temperatures of 500–5000 K has been the subject of active scientific research over the past few decades. However, various experimental and theoretical methods do not provide consistent results. In this work, we have applied the restricted open‐shell Kohn–Sham (ROKS) method for first principles molecular dynamics of dense hydrogen after thermal excitation to the first singlet excited state. The Wannier localization method has allowed us to analyze the exciton dynamics in this system. The model shows that a key mechanism of the transition is associated with the dissociation of electron‐hole pairs, which allows explaining several stages of the transition of fluid H2 from molecular state to plasma. This mechanism is able to give a quantitative description of several experimental results as well as to resolve the discrepancies between experimental studies.

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“…Introduction. The behavior of hydrogen under conditions of extreme compression (100-400 GPa) and high temperatures (1000-4000 K) has been studied for quite a long time [1][2][3][4][5] but its theoretical description still poses many unresolved questions [6][7][8]. One of these problems is the transition of compressed hydrogen in both solid and fluid states into a conducting state (metallization of solid hydrogen was predicted a long time ago [9]).…”

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confidence: 99%