High-pressure melting curve of hydrogen (original) (raw)
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Turnover of the melting line of highly compressed molecular hydrogen
2013
Conventional molecular dynamics simulation has been used to determine melting temperature of highly compressed classical molecular hydrogen in a wide range of pressures and temperatures using non-empirical atom-atom potentials approximation. It is shown that the raise of melting temperature with increasing pressure becomes more and more smooth and at megabar pressures its slope goes negative. We discuss the reasons of this turnover and analyze connection of this effect with the parameters of chemical bonding in H2.
Communication: Dynamical and structural analyses of solid hydrogen under vapor pressure
The Journal of chemical physics, 2015
Nuclear quantum effects play a dominant role in determining the phase diagram of H2. With a recently developed quantum molecular dynamics simulation method, we examine dynamical and structural characters of solid H2 under vapor pressure, demonstrating the difference from liquid and high-pressure solid H2. While stable hexagonal close-packed lattice structures are reproduced with reasonable lattice phonon frequencies, the most stable adjacent configuration exhibits a zigzag structure, in contrast with the T-shape liquid configuration. The periodic angular distributions of H2 molecules indicate that molecules are not a completely free rotor in the vapor-pressure solid reflecting asymmetric potentials from surrounding molecules on adjacent lattice sites. Discrete jumps of librational and H-H vibrational frequencies as well as H-H bond length caused by structural rearrangements under vapor pressure effectively discriminate the liquid and solid phases. The obtained dynamical and structur...
Journal of Low Temperature Physics, 1979
These are corrected to correspond to para-H2 and ortho-D2. The 4.2 K isotherm of H2 has been determined and compared to the extrapolated low-pressure isochore of Anderson and Swenson (AS). Deviations have led us to reanalyze the AS data. The 4.2 K isotherm and the isochores are used, with the aid of a Mie-Griineisen analysis, to determine P-V-T data for these solids up to 25 kbar. An analysis is presented which enables a determination of P-V-T-C~ for all values of C1, the ortho-para concentration. Results, including the Debye temperature, Griineisen constant, and bulk modulus, are presented both in tabulated and graphical form. We also present what we feel to be the best of the 4.2 K, zero-pressure molar volumes of disordered H2 and De as a function of C1. Our measurements show no indication of the premelting phase transition reported in recent Russian literature and a possible explanation is presented.
Proceedings of the National Academy of Sciences, 2010
Using quantum simulation techniques based on either density functional theory or quantum Monte Carlo, we find clear evidence of a first-order transition in liquid hydrogen, between a low conductivity molecular state and a high conductivity atomic state. Using the temperature dependence of the discontinuity in the electronic conductivity, we estimate the critical point of the transition at temperatures near 2,000 K and pressures near 120 GPa. Furthermore, we have determined the melting curve of molecular hydrogen up to pressures of 200 GPa, finding a reentrant melting line. The melting line crosses the metalization line at 700 K and 220 GPa using density functional energetics and at 550 K and 290 GPa using quantum Monte Carlo energetics.
Probing the Hydrogen Melting Line at High Pressures by Dynamic Compression
Physical Review Letters, 2008
We investigate the capabilities of dynamic compression by intense heavy ion beams to yield information about the high pressure phases of hydrogen. Employing ab initio simulations and experimental data, a new wide range equation of state for hydrogen is constructed. The results show that the melting line up to its maximum as well as the transition from molecular fluids to fully ionized plasmas can be tested with the beam parameters soon to be available. We demonstrate that x-ray scattering can distinguish between phases and dissociation states.
Highly Compressed Molecular Hydrogen Near the Melting Line
2001
We studied the radial and angular molecular distribution functions of high-density solid hydrogen in Monte Carlo computer simulation within non-empirical atom-atom potential (AAP) approximation. Lines of translational and orientational melting were located and compared with experiment. Significance of non-central short-range part of intermolecular repulsion and molecular non-rigidity in the description of translational and orientational phase transitions in dense condensed hydrogen was demonstrated.
Melting line of hydrogen at high pressures
Physical review letters, 2008
The insulator to metal transition in solid hydrogen was predicted over 70 years ago but the demonstration of this transition remains a scientific challenge. In this regard, a peak in the temperature vs. pressure melting line of hydrogen may be a possible precursor for metallization. However, previous measurements of the fusion curve of hydrogen have been limited in pressure by diffusion of hydrogen into the gasket or diamonds. To overcome this limitation we have used an innovative technique of pulsed laser heating of the sample and final peak in the melting line at P= 64.7 ± 4 GPa and T=1055 ± 20 K.