The delocalization of H in crystalline material, which was related to the quantum nature of the proton, was studied by means of path-integral Monte Carlo simulations at temperatures ranging from 50 to 300K. The Si-H interaction potential was fitted to the results of earlier pseudopotential density functional calculations. It was found that the lowest-energy position for H corresponded to the bond-center site; with an average distance, of the proton to the Si-Si axis, of more than 0.015nm. At 50K, the proton delocalization around the bond-center site amounted to 0.00044nm2. Anharmonicity of the interatomic potential acted so as to increase this delocalization with respect to a 1-particle harmonic approximation.

C.P.Herrero, R.Ramírez: Solid State Communications, 1996, 97[5], 319-22