Hydrocarbons under Pressure: Phase Diagrams and Surprising New Compounds in the C-H System

Anastasia S. Naumova, Sergey V. Lepeshkin, Artem R. Oganov

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13 Citations (Scopus)


Understanding the high-pressure behavior of the C-H system is of great importance due to its key role in organic, bio-, petroleum, and planetary chemistry. We have performed a systematic investigation of the pressure-composition phase diagram of the C-H system at pressures up to 400 GPa using evolutionary structure prediction coupled with ab initio calculations and discovered that only saturated hydrocarbons are thermodynamically stable. Several stable methane-hydrogen cocrystals are predicted: 2CH4 ∗ H2, earlier obtained experimentally, is predicted to have the I4/m space group and 2-90 GPa stability range at 0 K, and two new thermodynamically stable compounds 2CH4 ∗ 7H2 (P-3m1 space group) and CH4 ∗ 9H2 (Cm space group), and are potential energy storage materials. The P21/c phase of methane is predicted to be stable at pressures <8 GPa; bulk graphane (CH) was shown to be thermodynamically stable at 7-18 and 18-50 GPa and 0 K in the P-3m and Cmca phases, respectively; polyethylene is shown to have a narrow field of stability. We report the p-T-x phase diagram of the C-H system and p-T phase diagram of CH4.

Original languageEnglish
Pages (from-to)20497-20501
Number of pages5
JournalJournal of Physical Chemistry C
Issue number33
Publication statusPublished - 22 Aug 2019


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