[Mesa-users] problems with trace elements diffusion

[Ana Antonini]

Dear Mesa users,

We've been working on a project using MESA version r-15140 and have run
into a problem we can't seem to solve.

We've been trying to investigate if the results from Horowitz & Caplan
(2021) can be reproduced with stellar evolution models, but despite trying
a broad combination of controls and parameters, we can't get our uranium
isotopes to actually diffuse.
Some of the things we tried:

   -  setting a more rigorous tolerance for "diffusion_X_tot_atol" and
   "diffusion_X_tot_rtol"
   - forcing diffusion by setting "diffusion_class_factor" higher for the
   uranium species
   - limiting the timestep by using "diffusion_dt_div_timescale"
   - adding the timestep controls used in the wd_diffusion test_suite to
   our work
   - both using and not using the full net
   - setting the class_factor to zero for all classes except uranium

I'm attaching our inlist as well as other pertinent files and would greatly
appreciate any ideas you might offer or even just a confirmation that  MESA
is indeed capable of doing diffusion for species with such a low abundance.

Kind  Regards,
A. Antonini
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