The path-integral method of quantum simulation is applied to an empirical model for hydrogen in niobium. Results for the density distribution of D, H, and the positive muon over the unit cell show the dramatic increase of quantum effects along this series. Calculations on the activation energy for diffusion confirm the importance of excited states at high temperature pointed out by Emin, Baskes, and Wilson and suggest that hydrogen diffusion is approximately classical in this regime.

• Received 4 August 1986

DOI:https://doi.org/10.1103/PhysRevLett.58.563