Wei’s paper on hydrogen diffusion on metal surfaces have been accepted in PRL! In this work, hydrogen diffusion on a variety of metal surfaces has been studied with DFT. We found many of these processes can be categorized as having barriers with conventional “parabolic-tops” or unconventional “broad-tops”. On the broad-top barriers, a temperature regime at which both classical hopping and deep tunnelling are supported simultaneously is discovered, as well as its physical origin. The unique behavior observed here has led to a series of implications both theoretically and experimentally. Please see the publications page for more details.