Jump to content
Geochemist's Workbench Support Forum

Invariant point calculation failes


Frank Bok

Recommended Posts

Hi folks,

 

I've tried to model some invariant point in salt solutions and sometimes the workbench doesn't converge at the invariant point but swaps back and forth between the two mineral phases. Then it ends with messages like:

 

N-R didn't converge after 400 its., maximum residual = 7.65e-11, Xi = 0.4929
Cutting step size to find phase assemblage
Swapping Thenardite in for Mirabilite
Step 87, Xi = .4929 (2 iterations)
-- Can't converge, abandoning path.
-- Xi step is too small

I have attached a .rea example file, the output and a graphic. Maybe you can give me a hint?!

 

Best regards,

Frank

Invariant_point.rea

post-10208-0-04916900-1391418688_thumb.png

React_output.txt

Link to comment
Share on other sites

Hi Frank,

 

If you're using GWB10, you have some control over the parameters used in the Pitzer calculations. Using the pitz_precon command (accessible from Config - Iteration) you can change the maximum number of passes through the Pitzer preconditioning loop before the Newton-Raphson iteration begins. This value defaults to 10, but decreasing it can sometimes help the program to converge. If you change the value to 5, your model will run to completion, though it still has some weird oscillatory behavior.

 

You can read more about the new pitz_precon command, as well as pitz_relax and pitz_dgamma in the GWB Reference Manual.

 

Hope this helps get you started,

 

Brian Farrell

Geochemist

Aqueous Solutions LLC

Link to comment
Share on other sites

Hi Brian,

 

thank you for the information. Beside of the oscillation I get the invariant point.

 

Best regards,

Frank

Link to comment
Share on other sites

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.

Guest
Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.

Loading...
×
×
  • Create New...