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[OLD] Pitzer database

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From: Barry R. Bickmore

Subject: Pitzer Database

I am new to GWB, and I am attempting to alter the Pitzer database to include some interaction coefficients I've had to estimate. In the estimation methods I'm using I have to assume only binary interactions between cations and anions, so Beta(0), Beta(1), and Alpha(1) are the only parameters I can use. When I am inputting these data into the database, can I include only the cation-anion interaction sets, or do I need to include blocks for all possible cation-cation, anion-anion, and ternary interactions, setting the coefficients to zero?

From: Craig Bethke

Subject: Re: Pitzer Database

You can simply omit the remaining virial coefficients from your dataset; there is no need to set them to zero.

From: Barry R. Bickmore

Subject: More Pitzer Problems

I have one more issue to deal with before I think I'll be up to speed on the Pitzer database. In the GWB 3.0 manual it gives a certain format for the Pitzer data where each virial coefficient also comes with up to 4 constants one can plug into a polynomial to come up with the temperature dependence. The example in the manual has the constants (c1-c4) for Beta(0) in the Na+ Cl- block listed as 0.008946, -777.03, -4.4706, and -3.3158E-6. However, in the database I'm trying to customize, the block appears as follows:

Na+ Cl-

beta0 = 0.0765 beta1 = 0.2664 beta2 = 0.0000

alpha1 = 2.0 alpha2 = 0.0

db0/dt = 0.716E-03 d2b0/dt2 = -0.150E-04

db1/dt = 0.700E-03 d2b1/dt2 = 0.214E-03

db2/dt = 0.000E+00 d2b2/dt2 = 0.000E+00

I can't detect any relationship between the constants in the manual, and the derivative values listed in the database. Furthermore, there are a max of 2 coefficients, rather than 4, listed in the database. The db/dt term seems understandable if there is a linear change in the coefficient with temperature, but I'm lost on the second derivative term. Can someone explain to me how to interpret the database values?

From: Craig Bethke

Subject: Re: More Pitzer Problems

It looks like you may not be using the correct dataset as a template. The GWB includes two datasets for the virial model: thermo_hmw.dat and thermo_phrqpitz.dat. These are up-to-date in that they use the current virial formalism. There are also two datasets distributed with the software that have not been supported for quite some time: thermo_pitzer.dat and thermo_hdata.dat (see p. 6 of the GWB manual). These are not recommended for use and are included only for compatibility with very early versions of the GWB. Perhaps you picked up one of the latter?

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