Liquid methane at extreme temperature and pressure: Implications for   models of Uranus and Neptune
  We present large scale electronic structure based molecular dynamics simulations of liquid methane at planetary conditions. In particular, we address the controversy of whether or not the interior of Uranus and Neptune consists of diamond. In our simulations we find no evidence for the formation of diamond, but rather sp2-bonded polymeric carbon. Furthermore, we predict that at high tem- perature hydrogen may exist in its monoatomic and metallic state. The implications of our finding for the planetary models of Uranus and Neptune are in detail discussed. 
Dorothee Richters and Thomas D. K\"uhne
physics.chem-ph astro-ph.EP cond-mat.stat-mech physics.comp-ph