Abstract
The renormalisation of the hydrogen transfer integrals in niobium and tantalum due to the displacement clouds dressing the particles is investigated quantitatively. An auxiliary matrix tau (T) is introduced and values of its elements are presented, which permits evaluation of the renormalisation parameter S(T) once the self-trapping displacements around the hydrogen impurities are known. Estimates are given of S(T) for self-trapped H (and D) in Nb and Ta. A microscopic model is described for treating H trapped at O impurities in Nb and the renormalisation parameter is extracted for this case.