Methane under pressure: dissociation reactions from ab initio simulation*

Using ab initio molecular dynamics [1], we have investigated the stability of methane under pressure up to $\sim 24$ GPa and in the temperature range $2-4000$ K, studied in recent diamond anvil cell experiments [2]. In particular, we have explored the possible formation of alkanes from methane dissociation. We have calculated structural and vibrational properties, and compared the relative stability of several hydrocarbons mixtures. Our results show that the temperature is the main driving force for methane dissociation, with pressure enhancing the formation of higher hydrocarbons, at temperatures where dissociation is observed. [1] Qbox code: http://eslab.ucsvais.edu [2] A. Kolesnikov, Kutcherov VG. and Goncharov AF. {\it Nature Geoscience} , (2009) {\bf 8} (566-570)