Aromaticity, closed-shell effects, and metallization of hydrogen
Ivan I Naumov1, Russell J Hemley
1Geophysical Laboratory, Carnegie Institution of Washington , 5251 Broad Branch Road NW, Washington, D.C. 20015, United States.
Accounts of Chemical Research
|November 5, 2014
Summary
Compressed hydrogen transforms into unexpected layered structures, challenging previous theories. This discovery reveals novel chemical bonding and delayed metallization due to electronic stability.
Area of Science:
- Condensed matter physics
- Quantum chemistry
- Materials science
Background:
- Previous theories predicted simple, symmetric structures for hydrogen at high pressures.
- Experimental and theoretical studies have challenged these predictions.
Purpose of the Study:
- To explain the formation of unexpected layered structures in compressed hydrogen.
- To investigate the role of chemical bonding in dense hydrogen phases.
- To understand the mechanism of pressure-induced metallization.
Main Methods:
- Theoretical calculations using molecular quantum chemistry and solid-state physics.
- Analysis of low-dimensional model systems (H6 rings, graphene-like monolayers).
- Consideration of electronic band structure and closed-shell effects.
Main Results:
- Compressed hydrogen (200-350 GPa) forms layered structures with distorted graphene sheets.
- These structures exhibit unique chemical bonding, deviating from close-packed arrangements.
- A closed-shell electronic effect in model systems and observed structures delays metallization.
- Metallization occurs upon further compression by disrupting the closed-shell electronic structure.
- Enhanced diamagnetic susceptibility suggests aromaticity in compressed hydrogen.
Conclusions:
- Chemical bonding forces govern the properties of dense hydrogen over a wide range of conditions.
- Layered structures and closed-shell electronic effects are key to understanding hydrogen's behavior at extreme pressures.
- Magnetic measurements can characterize aromaticity and electronic properties of compressed hydrogen.
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