English (United Kingdom)

https://curated-unify.zendy.io/wp-json/zendy-region/v1/featured_content/oa?rat=en

https://curated-unify.zendy.io/wp-json/zendy-region/v1/highlighted_journal/

Global: Zendy Plus annual

Presents the access of premium content as premium feature

Premium Content

Presents the keyphrase highlighting as premium feature

Keyphrase Highlighting

Presents the summarisation as premium feature

Summarisation

Insights

Presents the pdf analysis as premium feature

PDF Analysis

Presents the zaia usage as premium feature

ZAIA

Global: Zendy Tools annual

Global: Zendy Free Plan

Global: Zendy Tools monthly

Global: Zendy Plus monthly

The electric quadrupole-quadrupole ($\mathcal{E}_{qq}$) interaction isbelieved to play an important role in the broken symmetry transition from PhaseI to II in solid hydrogen. To evaluate this, we study structures adopted bypurely classical quadrupoles using Markov Chain Monte Carlo simulations of fccand hcp quadrupolar lattices. Both undergo first-order phase transitions fromrotationally ordered to disordered structures, as indicated by a discontinuityin both quadrupole interaction energy ($\mathcal{E}_{qq}$) and its heatcapacity. Cooling fcc reliably induced a transition to the P$a3$ structure,whereas cooling hcp gave inconsistent, frustrated and $c/a$-ratio-dependentbroken symmetry states. Analysing the lowest-energy hcp states using simulatedannealing, we found P$6_3/m$ and P$ca2_1$ structures found previously asminimum-energy structures in full electronic structure calculations. Thecandidate structures for hydrogen Phases III-V were not observed. Thisdemonstrates that $\mathcal{E}_{qq}$ is the dominant interaction determiningthe symmetry breaking in Phase II. The disorder transition occurs atsignificantly lower temperature in hcp than fcc, showing that the$\mathcal{E}_{qq}$ cannot be responsible for hydrogen Phase II being based onhcp.

Quadrupole Arrangements and the Ground State of Solid Hydrogen