  Numerical computations of stellar oscillations for models representative of
B-type stars predict fewer modes to be excited than observations reveal from
modern space-based photometric data. One shortcoming of state-of-the-art
evolution models of B-type stars that may cause a lack of excited modes is the
absence of microscopic diffusion in most such models. We investigate whether
the inclusion of microscopic diffusion in stellar models of B-type stars,
notably radiative levitation experienced by isotopes, leads to extra mode
driving by the opacity mechanism compared to the case of models that do not
include microscopic diffusion. We consider the case of slowly to moderately
rotating stars and use non-rotating equilibrium models, while we account for
(uniform) rotation in the computations of the pulsation frequencies. We
calculate 1D stellar models with and without microscopic diffusion and examine
the effect of radiative levitation on mode excitation, for both low-radial
order pressure and gravity modes and for high-radial order gravity modes. We
find systematically more modes to be excited for the stellar models including
microscopic diffusion compared to those without it, in agreement with
observational findings of pulsating B-type dwarfs. Furthermore, the models with
microscopic diffusion predict that excited modes occur earlier on in the
evolution compared to modes without it. In order to maintain realistic surface
abundances during the main sequence, we include macroscopic envelope mixing by
internal gravity waves. While radiative levitation has so far largely been
neglected in stellar evolution computations of B-type stars for computational
convenience, it impacts mode excitation predictions for stellar models of such
stars. We conclude that the process of radiative levitation is able to reduce
the discrepancy between predicted and observed excited pulsation modes in
B-type stars.
