  We present detailed evolutionary calculations focused on the evolution of
intermediate mass stars with 3 Msun < M < 9 Msun of metallicity typical of the
Large Magellanic Cloud (LMC), i.e. Z=0.008. We compare carefully the models
calculated by adopting a diffusive scheme for chemical mixing, in which nuclear
burning and mixing are self-consistently coupled, while the eddy velocities
beyond the formal convective core boundary are treated to decay exponentially,
and those calculated with the traditional instantaneous mixing approximation.
We find that: i) the physical and chemical behaviour of the models during the
H-burning phase is independent of the scheme used for the treatment of mixing
inside the CNO burning core; ii) the duration of the He-burning phase relative
to the MS phase is systematically longer in the diffusive models, due to a
slower redistribution of helium to the core from the outer layers; iii) the
fraction of time spent in the blue part of the clump, compared to the stay in
the red, is larger in the diffusive models. The differences described in points
ii) and iii) tend to vanish for M > Msun. In terms of the theoretical
interpretation of an open cluster stellar population, the differences
introduced by the use of a self-consistent scheme for mixing in the core with
adjacent exponential decay are relevant for ages in the range 80 Myr < t < 200
Myr. These results are robust, since they are insensitive to the choice of the
free-parameters regulating the extension of the extra-mixing region.
