No evidence of metallic methane at high pressure

Abstract

Recently reported superconductivity in lithium under pressure has renewed the interest in hydrogen and hydrogen-rich systems in the long standing quest for room temperature superconductivity. As the required metallization of pure hydrogen cannot be achieved within current experimental capabilities, it has been suggested that the chemical precompression exerted by heavier atoms in compounds with a large hydrogen content should lower the required pressures to attain the metallic transition in these alloys. Following the trend of analyzing group IVa hydrides, we present an ab initio analysis of pressure-induced metallization of methane. According to our calculations, the metallization of methane is not predicted to occur below 520 GPa, which corresponds to a compression factor of 7.5.

Acknowledgements

Finally, the authors would like to aknowledge Prof. N.W. Ashcroft for many useful discussions and suggestions. One of us, M.M.C., would like to thank the Spanish Ministry of Education and Science for providing a grant. Computational resources for this work were provided by the SGI/IZO-SGIker at the UPV/EHU (supported by the Spanish Ministry of Education and Science and the European Social Fund).

Notes

¹ r _s being defined as r _s =(3V/4π ZN)^1/3, where V is the volume of the unit cell at a given pressure, Z is the number of formula units of methane in the unit cell, and N is the number of valence electrons per CH₄ formula, which is equal to 8.