rockwebmaster Posted December 26, 2004 Share Posted December 26, 2004 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? Link to comment Share on other sites More sharing options...

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