GEMS Default Thermodynamic Database

The GEMS default Thermodynamic Database (TDB) is included for a broader applicability of GEM-Selektor and GEMS3K codes.

• TDB includes the PSI-Nagra chemical thermodynamic database converted into GEMS DComp/ReacDC formats (default).

• TDB also includes the SUPCRT92 (Slop98.dat) dataset imported into GEMS DComp format (complementary).
  

• Third-party TDB plugins for specific applications (e.g. cement chemistry, nuclear engineering, ore petrology) are available.
  

• In GEM-Selektor code, the thermodynamic data for DCs is automatically corrected for temperature and pressure of interest.
  

• Thermodynamic data for wide T,P ranges can be exported into GEMS3K I/O files and thus into coupled reactive transport codes.

GEM-Selektor v.3 package is distributed with a default chemical thermodynamic database that consists of three parts: (i) "psi-nagra"; (ii) "supcrt"; and (iii) "3rd-party", selectable upon creation of modelling projects within GEMS "Elements" dialog. These parts can be selected separately or simultaneously when a new GEMS modeling project is created.

(i) The "psi-nagra" part has been imported from the PSI/Nagra 12/07 chemical thermodynamic database, which is a recent update of the previous Nagra-PSI chemical thermodynamic data base 01/01. This database covers the needs of geochemical modelling related to the nuclear waste disposal. In order to make the database also usable at moderately elevated temperatures and pressures, it was merged with a subset of the "supcrt" database.

(ii) The "supcrt" part consists of the imported very popular SUPCRT92 (Slop98.dat) dataset, which enables calculation of aqueous equilibria at temperatures up to 1000 ^oC and pressures up to 5 kbar for a wide range of species and chemical elements, also those not available in the "psi-nagra" part. The SUPCRT92 dataset that relies on the open SUPCRT92 code and the revised HKF EoS (Helgeson- Kirkham- Flowers  equation of state) is at present a "de facto" standard in geochemistry, supplied also completely or in part with many other codes (e.g. ChemApp, EQ3/6, GIBBS/Hch, Selektor-C/W).

(iii) The "3rd-party" part (optional) is represented by one or more third-party databases covering specific application fields (e.g. Cemdata'07 or HERACLES). The respective files can be downloaded separately and added into the default database folder in the actual GEM-Selektor installation.

GEM-Selektor supports a unique "hybrid" structure of thermodynamic database, comprised of the DComp and ReacDC formats. TDB parts in DComp format contain 'thermochemical' and/or 'equation of state' data for Dependent Components (DC). TDB parts in ReacDC format define the thermodynamic data for a DC via the properties of its reaction with other DCs with already known properties. The respective modules of GEM-Selektor code provide efficient tools for internally consistent extension of project thermodynamic databases, which is also enhanced by standalone codes such as PMATCHC.

Note that files in the default database folder ("/DB.default/") are write-protected in GEM-Selektor code in order to prevent an unitentional data loss or corruption, and to ensure a backward compatibility between different modelling projects. More technical details about that can be found in the GEM-Selektor help pages. 

References

Helgeson H.C., Kirkham D.H. and Flowers G.C. (1981): Amer. J. Sci. v. 281, p. 1249-1516.

Johnson J.W., Oelkers E.H. and Helgeson H.C. (1992): Comput. Geosci. v. 18, p. 899-947.

Shock E.L., Sassani D.C., Willis M. and Sverjensky D.A. (1997): Geoch. Cosmoch. Acta v. 61, p. 907-950 (and references therein).