How to extract Debye-Hückel parameters for all species from the database

[md.muniruzzaman]

Hello everybody,

I am wondering if there is a way to extract Debye-Hückel (A, B) parameters for all the species in the solution. I know that I can always use the basic functions DH_A and DH_B to extarct these parameters for selected species, which is somewhat a manual approach and I need to do species by speices basis. So, is there any smarter way to extract these values automatically for all the species present in a SOLUTION?

Any suggestions or tips would be highly appreciated.

Cheers.

[dlparkhurst]

Unfortunately, no, there is no function to extract a0 (the ion size parameter) or bdot (the ionic strength factor) for individual species. The DH_A and DH_B are temperature dependent constants from the Debye Huckel equation that are the same for all aqueous species; a0 and bdot are ion specific parameters.

-DH_A*z^2*mu^.5/(1 + DH_B*a0*mu^0.5) + bdot*mu

 

[md.muniruzzaman]

Hi David,

First of all, sorry for the mix-up between the parameters (smaller and capilal A and B )! But it seems you understood my point. Thanks for the clarification! So, it means if I want to extract these parameters (a0 or bdot), the only possible way would be to manually grab them from the database, right?

Thanks again!

[dlparkhurst]

Yes, I think you would have to do it manually.

Note that llnl.dat uses the same a0 and bdot parameters for all charged species, and one bdot for selected uncharged species. Also, Pitzer databases do not use a0 or bdot, nor does sit.dat.

[dlparkhurst]

I was writing other Basic functions, so I added DH_A0("H+") and DH_BDOT("H+"). No guarantees on when the next version is released, but we are working on it.

[md.muniruzzaman]

Hi David,

Thanks a lot again for the clarification, and for considering these basic functions in the new release. It would surely be helpful for my purpose of implementating the activity gradient flux term in Nernst-Planck based diffusive flux calculations. In this direction, I wonder if it would also be possible to have "Get" methods to extarct these parameters in PhreeqcRM.

Regards,
Munir

[dlparkhurst]

There is a GetLog10Gammas method, and the next version will have a GetLog10Molalities. I'm kind of sick of writing PhreeqcRM methods.

If that is not enough, you could always use the new functions and SELECTED_OUTPUT/USER_PUNCH to extract the values in a one-time run to get ready for the main calculation. The list of species is available from GetSpeciesNames.

[md.muniruzzaman]

Hi David,

No worries! It was only a suggestion for some future steps.....  The selected_output method in connection with the new function would be perfectly sufficient :)