Values of the Debye-Hückel A parameter for the SIT and the Pitzer models

[CST]

Does anyone know where I can find the value of the parameter A referring to the Debye-Hückel parameter when I am using the SIT model or the Pitzer model?
I looked in both databases sit.dat and pitzer.dat but I did not find anything.

Is this parameter implemented directly in PHREEQC?

Thank you,

[dlparkhurst]

The following Basic functions return Debye Huckel parameters:

APHI   The A(phi) parameter of the Pitzer formulation of aqueous thermodynamics at the current solution conditions.
 
DH_A   Debye-Hückel A parameter in the activity coefficient equation, (mol/kg) -0.5 .
 
DH_Av  Debye-Hückel limiting slope of specific volume vs. ionic strength, (cm 3 /mol) (mol/kg) -0.5 .
 
DH_B   Debye-Hückel B parameter in the activity coefficient equation, angstrom -1 (mol/kg) -0.5 .

For most databases, the temperature dependence of the parameters are hard coded within PHREEQC in the method calc_dialectrics in the file utilities.cpp. One exception is that llnl.dat provides a table of dh_a and dh_b for a range of temperatures, and the values are interpolated for the current temperature.

The other exception is that a parameterization for A(phi) for the Pitzer formulation can be defined in the PITZER data block with the option -aphi. The database ColdChem.dat uses -aphi to extend Debye-Huckel parameters to lower temperatures.

The following is excerpted from the Release Notes file http://water.usgs.gov/water-resources/software/PHREEQC/Phreeqc_ReleaseNotes.txt found at https://www.usgs.gov/software/phreeqc-version-3:

   PHREEQC: Added the ColdChem.dat database developed by Toner and
   Catling, Journal of Chemical & Engineering Data, 2017, DOI: 10.1021/
   acs.jced.6b00812. It is a comprehensive Pitzer model in the Na-K-Ca-Mg-
   Cl system valid for low temperature, from 298.15 to < 200 K.
   PHREEQC was modified to allow definition of the temperature dependence
   of A(phi) in the Pitzer formulation through a new option, -APHI, in
   the PITZER keyword. The coefficients of the APHI expression are the
   same as the temperature dependence of other Pitzer parameters.
   A new Basic function, APHI, has been added to give the value of
   the parameter in the current calculation.
 

[CST]

Thank you very much for your reply. You answer to all my questions.