Atomic diffusion processes may significantly change the distribution of chemical elements inside the stars. Being slow, these processes gain importance in zones where the mixing processes are very weak or absent, i.e., in the radiative zones. However, the modified abundances in these stable zones may contaminate those where mixing occurs. In some cases the internal structure of the star can be affected, mainly through local opacity changes that depend on the local chemical composition. One of the main ingredients in evaluating diffusion velocities in stars is the radiative acceleration, which accounts for the momentum transfer from the photon flux to the atoms. Radiative accelerations are closely dependent on the atomic properties of each species entering the mixture of the local plasma, and thus their calculations are intricately related to the available atomic data and opacity tables. We give an overview of the various methods used to compute radiative accelerations, and show some examples of the crucial roles played by large atomic and opacity databanks in their calculations.