AbstractThe windforce acting upon a host atom and the impurities Ta, Cr, and Ni in niobium is calculated in a finite cluster model. In this model all strong and multiple scattering effects up tolmax= 2 are preserved. Special attention is given to the influence of the vacancy, the cluster size, and of charge transfer. A positive windforce is found, in accordance with experiment, so that this appears to be not directly related to a hole current contribution, contrary to what is believed commonly.