Based upon full-electron ab initio calculations, orientational preferences and correlation of the atop-to-atop motions of H2O on Al{100} were found which originated from the symmetry match between H2O and the surface square lattice. Theoretical evidence was provided which showed that the favored mechanisms could be classical hopping coupled with molecular flipping or in-plane reorientations; having reduced energy barriers when compared to those of simple translational motions. Quantum tunnelling-assisted motion was not favored for H2O via nearest-neighbor diffusion.

Symmetry-Mediated H2O Diffusion on Al{100}. J.Li, Y.Li, S.Zhu, F.Wang: Physical Review B, 2006, 74[15], 153415 (4pp)