Résumé
Atomic diffusion, including the effect of radiative accelerations on individual elements, leads to strong variations of the chemical composition inside the stars as well as of the evolution of surface abundances. Accumulation in specific element layers, which are the main contributors to the local opacity, leads to hydrodynamical instabilities that modify the internal stellar structure and surface abundances. We show that the variations of the chemical composition induced by atomic diffusion can lead to an increase of the Rosseland opacity in some layers by up to a factor of three, and have important effects on the internal stellar mixing. These processes can no longer be neglected in stellar evolution models as the observations are more and more precise, especially with the future space missions TESS and PLATO.