Convergence problem chemistry

Hello, everyone,

I was running a water-rock interaction model with Toughreact. The runlog.out file prompted "Warning: chemistry did not converge at node A1114 (routine NEWTONEQ), Non-convergence type:   relative  Node temperature ....."

I adjusted the loop limit (MAXITCH) and tolerance (TOLCH) in the solute.inp file, which was of no effect. 

When I run a long-term simulation, the time step size is always reduced to a value close to zero at a certain moment.

I am also wondering how to use chdump.out for debugging.

Hope someone could help me out of these problems.


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  • I am having the same problem.

    Making tolerance extremely high (1E+3) resulted in a very very small time step, and it never ends.

    I am sorry for not a helpful reply, but hope somebody can explain this :(

  • Usually the reasons for nonconvergence are:

    1. Time step too large - set rcour to 0.5 (cfl condition).

    2. Chemical system overdetermined. Look at mineral assemblages.

    3. Ionic strength increasing to outside range during iteration. Try setting stimax to between 2-8.

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    • Eric Sonnenthal 

      I'm having similar difficulties. Setting rcour to 0.5 doesn't help, ionic strength also isn't the problem.

      What do you mean "Look at mineral assemblages"? Some of the simulations work, some don't and I cannot figure out the problem. Do you have any ideas/hints?

      I have attached an excerpt from the chdump file, if that helps.

      Any help would be appreciated!

  • Hi, Eric.  I just noticed your reply. I managed to get around this problem.  Thanks for your help~

  • Jaeshik Chung  Good luck 😂

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