Parallel replica dynamics and minimum energy path calculations were used to study the diffusion mechanisms of H2 in face-centered cubic C60. Isolated interstitial H2 molecules bound preferentially to the lattice octahedral sites and diffused by hopping between octahedral and tetrahedral sites. The simulations revealed an unexpected mechanism which involved an H2 molecule that diffused through an already occupied octahedral site; thus creating an H2 dimer with a lower activation barrier than that for diffusion into an empty octahedral site. Kinetic Monte Carlo simulations of a lattice model which was based upon these mechanisms indicated that events which involved dimers greatly enhanced the self-diffusion rates of interstitial H2 in face-centered cubic C60.

Mechanisms and Rates of Interstitial H2 Diffusion in Crystalline C60. B.P.Uberuaga, A.F.Voter, K.K.Sieber, D.S.Sholl: Physical Review Letters, 2003, 91[10], 105901 (3pp)