Metallic_hydrogen - Wikiparency

# Metallic hydrogen  ## Microsims — three.js ### Metallic hydrogen (three.js) <div class="microsim-player"> <iframe src="https://wikitube-3d-microsims.netlify.app/Metallic_hydrogen.html" width="100%" height="620" frameborder="0" loading="lazy" sandbox="allow-scripts allow-same-origin" title="Metallic hydrogen — three.js microsim"></iframe> </div> **Open it full-screen:** [Metallic_hydrogen.html](https://wikitube-3d-microsims.netlify.app/Metallic_hydrogen.html) · library `threejs` · route `microsim/threejs/` ### Related microsims Live sims on neighbouring articles: - [[Hydrogen_atom]] - [[Diatomic_molecule]] - [[Ammonia]] - [[Hydrogen_line]] *Sim hosted off-article; the article owns the reference, not the runtime (WIKI_RULES §10.4). Placed by `g08_place_microsims.py`.*  ## Overview Compress hydrogen far enough and the molecular solid stops being molecular. The H2 dumbbells come apart, the electrons stop belonging to particular nuclei, and an insulating crystal becomes an atomic metal. Eugene Wigner and Hillard Huntington predicted this in 1935 and estimated that about 25 GPa would be enough. The real figure is at least an order of magnitude higher, and ninety years later the transition has still not been uncontroversially achieved in a laboratory. Read that literally rather than as modesty. Hydrogen has been squeezed past 400 GPa in diamond anvil cells and made to conduct. It has not been shown, to the satisfaction of the field as a whole, to have become the atomic metal Wigner and Huntington described. The one place it certainly exists is inside Jupiter and Saturn, as a liquid, where nobody can reach it. ## The physics Phase I, the ambient solid, is a hexagonal close-packed lattice of H2 molecules behaving as free quantum rotors. In the rotational ground state a molecule's charge distribution is spherically symmetric, so the crystal carries no orientational information: it is a lattice of spheres. Phase II is where that changes, and the change is worth stating precisely. Above roughly 110 GPa at low temperature the molecules stop rotating freely and lock to particular directions. This is the broken-symmetry phase, and the symmetry it breaks is orientational, not structural: the lattice sites do not move, the objects sitting on them merely stop being round. Thermal motion restores rotation, so the I-II boundary leans to higher pressure as temperature rises. Phase III, above about 150 GPa at low temperature, announces itself with an enormous jump in infrared vibron intensity as charge shifts along the bonds. Phase IV, above about 220 GPa near room temperature, alternates graphene-like sheets with layers still recognisably molecular, and phase V continues that ordering above about 325 GPa. These boundaries are approximate, and everything above about 400 GPa is theoretical rather than measured. Metallisation itself is geometric. At ambient pressure the H2 bond is about 0.74 A while the nearest neighbouring proton is several angstroms away, so the bond-to-gap ratio is around 0.2 and "which two protons form a molecule" has an obvious answer. Pressure barely touches the bond, held by a strong covalent pair, while it collapses the lattice around it. The two lengths converge, and when they become comparable every proton has identical neighbours, molecular identity is gone, and protons sit in a shared electron sea. Ashcroft argued in 1968 that such a metal ought to be a high-temperature superconductor: the proton is light, so phonon frequencies are enormous and electron-phonon coupling strong. Nobody has tested that on hydrogen itself, but it is still why the field is funded, and it is the direct ancestor of the hydride superconductors, which use heavier atoms to chemically precompress hydrogen into reach. The status of the transition is genuinely contested. Dias and Silvera reported in *Science* in 2017 that hydrogen at 495 GPa and 5.5 K became reflective, and read this as solid atomic metallic hydrogen. Published comments from Goncharov and Struzhkin and from Eremets and Drozdov argued that the reflectance is equally consistent with the alumina coating on the diamond culets or the stressed diamond itself, and that the pressure calibration is uncertain enough that the true value may have been well below 400 GPa. The authors replied. The sample was then lost when the diamonds failed, so the measurement has never been re-examined and no independent group has reproduced it; the paper carries an erratum and has not been retracted. Loubeyre, Occelli and Dumas reported in 2020 an abrupt gap collapse near 425 GPa, but their claim is deliberately narrower: a probable metallisation *within the molecular solid*, which is not the Wigner-Huntington atomic transition. Static compression in anvil cells and dynamic compression in shock and ramp experiments probe different temperatures and disagree about where the insulator-to-metal line sits. There is no single "pressure required for metallic hydrogen", because molecular gap closure and atomic dissociation are different transitions. Jupiter and Saturn are where the material actually matters, and the distinction from the laboratory problem is often blurred. Most of Jupiter's mass is hydrogen at one to forty megabars and thousands of kelvin, far above the melting line. What exists there is *liquid* metallic hydrogen, conducting and convecting, and it drives the dynamo behind the planetary magnetic field. Juno-era interior models put the crossover inside a helium-rain layer spanning roughly 93 to 443 GPa: a gradual, compositionally messy change in a hot fluid, not the sharp cold solid-state transition that diamond anvils chase. ## Controls -> what each maps to | Control | Maps to | Range / values | Physical meaning | |---|---|---|---| | pressure | P | 0 to 600 GPa | The master control; walks the whole phase sequence. Wigner and Huntington's 25 GPa sits in the first four percent of the slider | | temperature | T | 1 to 20000 K, logarithmic | Destroys orientational order, and crosses the melting line into the fluid and then into liquid metallic hydrogen | | lattice | N cells per side | 3 to 7 (36 to 392 sites) | How much of the hcp lattice is built | | electron sea | -- | on / off | The point cloud: electrons bound to individual molecules, or delocalised across the lattice | | orientation vectors | -- | on / off | Draws the molecular axes as rods, which is what makes the phase II ordering legible | | phase diagram | -- | on / off | The schematic P-T inset, with the Jupiter marker on it | | Jupiter interior | P, T | button | Jumps to 200 GPa (2 Mbar) and 6600 K, on Jupiter's adiabat | | running | -- | on / off | Pauses libration, thermal motion and rotation | | reset | -- | button | Restores pressure and temperature and rebuilds the lattice | The HUD's headline live quantity is the ratio of the intramolecular H-H bond length to the nearest intermolecular H...H contact. It starts near 0.22 and is driven toward 1 by pressure alone. It is computed from the running equation of state rather than scripted, and a ratio of 1 is dissociation. ## Learning objective After playing, a learner can say what actually distinguishes phase II from phase I -- that it is an orientational ordering, not a structural rearrangement -- explain metallisation as the convergence of the bond length and the intermolecular gap, state separately what is claimed and what is disputed about the 2017 result, and distinguish the liquid metallic hydrogen that fills Jupiter from the solid atomic phase that laboratories are chasing. ## Limits and connections The equation of state is in two pieces. Below about 119 GPa it is a measured Vinet fit to static-compression data; above that it blends into a DFT and quantum Monte Carlo power law, because no measurement anchors the higher range. Both are cold-curve forms with no thermal expansion term, so densities at Jupiter-like temperatures are overestimates, and the HUD flags that whenever the state is hot. The phase boundaries above 400 GPa are drawn as predicted rather than measured, and the inset is schematic throughout; the dissociation threshold alone moves by more than a hundred gigapascals across published calculations. The bond that resists all this compression is the ordinary covalent bond of [[Diatomic_molecule]], and the electron sea it finally dissolves into is what happens when the bound states of [[Hydrogen_atom]] stop being bound to anything in particular. ## Wikipedia : Wikitube **Strict pair:** [Wikipedia](https://en.wikipedia.org/wiki/Metallic_hydrogen) : [Wikitube](https://en.wikitube.io/wiki/Metallic_hydrogen) ## Previous hub tags Tree parent: [[Hydrogen]]. Legacy hubs: `HYDROGEN`. --- *Created 2026-08-05 - append-only - portal-microsim-pass to WIKI_REPOPULATION_PROTOCOL v1.0 section 5 - 0 deletions*