Thermodynamic anomalies and three distinct liquid-liquid transitions in warm dense liquid hydrogen

Abstract

The properties of hydrogen at high pressure have wide implications in astrophysics and high-pressure physics. Its phase change in the liquid is variously described as a metallization, H2-dissociation, density discontinuity or plasma phase transition. It has been tacitly assumed that these phenomena coincide at a first-order liquid-liquid transition (LLT). In this work, the relevant pressure-temperature conditions are thoroughly explored with first-principles molecular dynamics. We show there is a large dependency on exchange-correlation functional and significant finite size effects. We use hysteresis in a number of measurable quantities to demonstrate a first-order transition up to a critical point, above which molecular and atomic liquids are indistinguishable. At higher temperature beyond the critical point, H2-dissociation becomes a smooth cross-over in the supercritical region that can be modelled by a pseudo-transition, where the H2-2H transformation is localized and does not cause a density discontinuity at metallization. Thermodynamic anomalies and counter-intuitive transport behavior of protons are also discovered even far beyond the critical point, making this dissociative transition highly relevant to the interior dynamics of Jovian planets. Below the critical point, simulation also reveals a dynamic H2-2H chemical equilibrium with rapid interconversion, showing that H2 and H are miscible. The predicted critical temperature lies well below the ionization temperature. Our calculations unequivocally demonstrate that there are three distinct regimes in the liquid-liquid transition of warm dense hydrogen.

arXiv comment34 pages, 7 figures, with Supplementary Material

References in corpus (35)

• Van der Waals Density Functional for General Geometries
• Van der Waals density functionals applied to solids
• Observation of the Wigner-Huntington Transition to Solid Metallic Hydrogen
• A superconductor to superfluid phase transition in liquid metallic hydrogen
• A quantum fluid of metallic hydrogen suggested by first-principles calculations
• Molecular Dissociation in Hot, Dense Hydrogen
• Thermophysical properties of warm dense hydrogen
• Electronic transport coefficients from ab initio simulations and application to dense liquid hydrogen
• Nuclear Quantum Effects and Nonlocal Exchange-Correlation Functionals Applied to Liquid Hydrogen at High Pressure
• A First-order Phase Transition to Metallic Hydrogen
• Structure and phase boundaries of compressed liquid hydrogen
• Phase diagram of hydrogen and a hydrogen-helium mixture at planetary conditions by Quantum Monte Carlo simulations
• Quantum simulation of low-temperature metallic liquid hydrogen
• Towards a Predictive First-Principles Description of Solid Molecular Hydrogen with Density-Functional Theory
• Quantum Monte Carlo Simulation of the High-Pressure Molecular-Atomic Crossover in Fluid Hydrogen
• Observability of a projected new state of matter: a metallic superfluid
• High-pressure behavior of dense hydrogen up to 3.5 TPa from density functional theory calculations
• Distinct metallization and atomization transitions in dense liquid hydrogen
• Evidence for percolation diffusion of cations and material recovery in disordered pyrochlore from accelerated molecular dynamics simulations
• The role of van der Waals and exchange interactions in high-pressure solid hydrogen
• Prediction of Stable Ground-State Lithium Polyhydrides under High Pressures
• Low temperature phase diagram of hydrogen at pressures up to 380 GPa. A possible metallic phase at 360 GPa and 200 K
• Striking Isotope Effect on the Metallization Phase Lines of Liquid Hydrogen and Deuterium
• Public Debate on Metallic Hydrogen to Boost High Pressure Research
• New Phases and Dissociation-Recombination of Hydrogen Deuteride to 3.4 Megabar
• Lattice stability and high pressure melting mechanism of dense hydrogen up to 1.5 TPa
• A simple thermodynamic model for the hydrogen phase diagram
• Local structure in dense hydrogen at the liquid-liquid phase transition by Coupled Electron-Ion Monte Carlo
• Predicted reentrant melting of dense hydrogen at ultra-high pressures
• Prediction of a Mobile Solid State in Dense Hydrogen under High Pressures
• Appraisal of the realistic accuracy of Molecular dynamics of high pressure hydrogen
• Theory of high pressure hydrogen, made simple
• Anomalies in non-stoichiometric uranium dioxide induced by pseudo-phase transition of point defects
• Non-congruent Phase Transitions in Cosmic Matter and in the Laboratory
• Theoretical assessment on the possibility of constraining point defect energetics by pseudo-phase transition pressures

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• Non-adiabatic effects and exciton-like states during insulator-to-metal transition in warm dense hydrogen
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• The Observed Vibron Shift in Helium-Hydrogen Mixtures are due to Quantum Nuclear and Localisation Effects, not bonding
• Hydrogen liquid-liquid transition from first principles and machine learning
• Accurate and thermodynamically consistent hydrogen equation of state for planetary modeling with flow matching
• Prediction of Superionic State in LiH2 at Conditions Enroute to Nuclear Fusion
• Pressure induced Structure Change and Anomalies in Thermodynamic Quantities and Transport Properties in Liquid Lithium Hydride
• A Denser Hydrogen Inferred from First-Principles Simulations Challenges Jupiter's Interior Models
• Geometry-Based Neural-Network Prediction of Electron Localization Function Topology in Dense Hydrogen
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