Read more about the team’s work on dense hydrogen in JCP

Dense hydrogen, despite the apparent simplicity of its component parts, is a very challenging system. Experimentalists are faced with the dual difficulties of sample preparation and analysis, while theorists must deal with the absence of good experimental structural models and the lightness of protons leading to strong quantum dynamical effects. In spite of these challenges, understanding this fundamental system remains an important area of study, as dense hydrogen comprises a large fraction of the universe in the form of stars and planets. Results of both experimental and theoretical studies of dense hydrogen reveal a surprising richness of behavior in this complex and intriguing system.

This series of four papers presents a fresh look at molecular hydrogen under pressure and its transition from a molecular to a monatomic, metallic state. In this series, the authors provide a conjoined physical and chemical view of hydrogen’s behavior as its density increases to scales both achievable in the laboratory and observed in stars and planets. Using a numerical laboratory of the best static structures calculated for hydrogen, they find in it an approach to metallization that preserves some features of diatomic molecules as well as opposing effects influencing distances in the compressed solid – a physical one of containment, and an orbital/chemical one of essentially donor-acceptor bonding between hydrogen molecules (making a connection to the side-on bonded dihydrogen organometallics). They also explore a model with lovely symmetry that makes a single-parameter transition between a molecular solid and a highly compressed monatomic one. These four papers, a physics and chemistry collaboration, shape a new, deeper understanding of hydrogen under pressure.

Highlighted JCP papers by Nobel laureate Roald Hoffmann and colleagues:

A fresh look at dense hydrogen under pressure: 1. An introduction to the problem, and an index probing equalization of H-H distances
Vanessa Labet, Paulina Gonzalez-Morelos, Roald Hoffmann, N. W. Ashcroft
J. Chem. Phys. 136, 074501 (2012)

A fresh look at dense hydrogen under pressure: 2. Chemical and physical models aiding our understanding of evolving H-H distances
Vanessa Labet, Roald Hoffmann, and N. W. Ashcroft
J. Chem. Phys. 136, 074502 (2012)

A fresh look at dense hydrogen under pressure: 3. Two competing effects and the resulting intra-molecular H-H separation in solid hydrogen under pressure
Vanessa Labet, Roald Hoffmann, N. W. Ashcroft
J. Chem. Phys. 136, 074503 (2012)

A fresh look at dense hydrogen under pressure: 4. Two structural models on the road from paired to monatomic hydrogen, via a possible non-crystalline phase
Vanessa Labet, Roald Hoffmann, N. W. Ashcroft
J. Chem. Phys. 136, 074504 (2012)

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