The jump-rate constants of atomic H and D in B-doped crystalline material were calculated by using quantum transition-state theory which was based upon the path-integral centroid formalism. A break in the slope of the Arrhenius plot for the jump rate of H was predicted to occur about 60K. This reflected a cross-over, from thermally activated quasi-classical motion over a barrier, to thermally assisted quantum tunnelling; in good agreement with experimental results. In the case of D, no deviation from Arrhenius behavior was found at temperatures down to 30K. It was shown that the defect complex which underwent quantum tunnelling consisted of H, B and the nearest Si atoms.

J.C.Noya, C.P.Herrero, R.Ramírez: Physical Review Letters, 1997, 79[1], 111-4