  Aims. Atomic diffusion, including the effect of radiative accelerations on
individual elements, leads to important variations of the chemical composition
inside the stars. The accumulation in specific layers of the elements, which
are the main contributors of the local opacity, leads to hydrodynamical
instabilities that modify the internal stellar structure and surface
abundances. Our aim is to study these effects and compare the resulting surface
abundances with spectroscopic observations Methods. We computed the detailed
structure of A-type stars including these effects. We used the Toulouse-Geneva
Evolution Code (TGEC), where radiative accelerations are computed using the
Single Valued Parameter (SVP) method, and we added double-diffusive convection
with mixing coefficients deduced from three-dimensional (3D) simulations.
Results. We show that the modification of the initial chemical composition has
important effects on the internal stellar mixing and leads to different surface
abundances of the elements. The results fit the observed surface chemical
composition well if the layers, which are individually mixed by
double-diffusive convection, are connected.
