  Diffusion of atoms can be important during quiescent phases of stellar
evolution. Particularly in the very thin inert envelopes of subdwarf B stars,
diffusive movements will considerably change the envelope structure and the
surface abundances on a short timescale. Also, the subdwarfs will inherit the
effects of diffusion in their direct progenitors, namely giants near the tip of
the red giant branch. This will influence the global evolution and the
pulsational properties of subdwarf B stars. We investigate the impact of
gravitational settling, thermal diffusion and concentration diffusion on the
evolution and pulsations of subdwarf B stars. Our diffusive stellar models are
compared with models evolved without diffusion. We constructed subdwarf B
models with a mass of 0.465 Msun from a 1 and 3 Msun ZAMS progenitor. The low
mass star ignited helium in an energetic flash, while the intermediate mass
star started helium fusion gently. For each progenitor type we computed series
with and without atomic diffusion. Atomic diffusion in red giants causes the
helium core mass at the onset of helium ignition to be larger. We find an
increase of 0.0015 Msun for the 1 Msun model and 0.0036 Msun for the 3 Msun
model. The effects on the red giant surface abundances are small after the
first dredge up. The evolutionary tracks of the diffusive subdwarf B models are
shifted to lower surface gravities and effective temperatures due to outward
diffusion of hydrogen. This affects both the frequencies of the excited modes
and the overall frequency spectrum. Especially the structure and pulsations of
the post-non-degenerate sdB star are drastically altered, proving that atomic
diffusion cannot be ignored in these stars.
