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React problems

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i am having problems with some calculations in react,

I am making a pH sliding of Zn++, i put the calculations with charge balance of Cl- and without charge balance.


I get error for the charge balance, and the calculations stop for the pH of ~8.5


"Caution: molality of Cl- component forced negative by charge balance: -2.782e-007

*N-R didn't converge after 400 its., maximum residual = 4.83e+121, Xi = 0.5800


Cutting step size to find solution

Residuals too large, 662-th interation

-- Didn't wake up, abandoning path"


For the sliding without the balance using react and even SpecE8 it can't compute from pH ~12.5 to ~13.8 but can compute for pH of 14.

Why is that?


I also find out that if i change the delxi from 0.01 to 0.001, making more dots the programs crushs and stops the compute arouth pH ~3.5 - ~6. Why is that? shouldn't it calculate the same for all?



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Apologies for the delay.


In your first script, as the error message indicates, you run out of Cl- for charge balance, and it is forced to negative concentrations. You can remedy this by either beginning with a higher anion concentration, or better yet, consider a base titration (NaOH for example), rather than a pH slide, as this avoids negative concentration issues. Unless this is a pure solution, it's a good idea to have some background electrolytes (Na, Cl).


The issue with the smaller reaction path steps occurs right when Zincite reaches saturation- you are essentially removing 1/10th the proton mass at each step, and this creates an unstable matrix when Zincite becomes supersaturated and React attempts to swap it in for the Zn++ matrix component. I'm not sure exactly why this happens, but this model is being run with a large charge imbalance- I recommend fixing the first model, with charge balance, as this should result in a model that is more stable overall. The same goes for the non-convergence issue at high pH.


I hope that helps,


Tom Meuzelaar

RockWare, Inc.

RockWare, Inc.

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