Re: [mesa-users] diffusion causing model to get stuck

[Aaron D. <aar...@gm...>]

Hi Jean,

I recommend trying the following control;

         ! treat at least this much at surface as a single cell for
purposes of

      diffusion_min_dq_at_surface = 1d-9

1d-9 is the default value.  Try setting it to a larger number, say 10^-4 or
10^-3.  This tells the diffusion module to use treat the outer fraction of
the star by mass as one zone in the diffuison calculation.  That
calculation can get messy near the stellar surface, especially in stars in
around ~1.5 Msun (as yours is) because they have a very thin -- or no --
surface convection.

Good luck!

Aaron






On Mon, Jun 5, 2017 at 3:42 PM, Jean McKeever <je...@nm...> wrote:

> Hello,
>
> I was trying to create a grid of models using the astero module and the
> grid got stuck on a particular point. After some testing of turning things
> on and off I have discovered that do_element_diffusion appears to be the
> culprit. For a 1.4 solar mass star with a metallicity of -.4, the model
> seems to get caught in a series of retries where dt keeps decreasing to be
> prohibitively small. This happens very early on in the model. If I turn off
> diffusion, the model proceeds normally.
>
> Can anyone provide insight as to why diffusion is causing the model to get
> stuck? I have attached some modified inlists and starting model to help
> reproduce this. I checked the newest version of mesa and it is still a
> problem in 9793.
>
> Thank you,
> Jean
>
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