Geochemistry computer codes

Most of the chemical processes discussed before (acid-base equilibria, precipitation-dissolution, neutralization, complexation, and oxidation-reduction) are interrelated that is, reactions of one type may influence other types of reactions, and consequently must be integrated into aqueous- and solution-geochemistry computer codes. 

A computer code is obviously not a model. A computer code that incorporates a geochemical model is one of several possible tools for interpreting water-rock interactions in low-temperature geochemistry. The computer codes in common use and examples of their application will be the main focus of this chapter. It is unfortunate that one commonly finds, in the literature, reference to the MINTEQ model or the PHREEQE model or the EQ3/6 model when these are not models but computer codes. Some of the models used by these codes are the same so that a different code name does not necessarily mean a different model is being used. 

Akinfiev N. N. (1976) Balance IBM computer code for calculating mineral aqueous solution-gas equilibria. Geochemistry 6, 882-890 (in Russian). 

Given these three areas of uncertainty chemical models need to be used with caution. The integration of organic and inorganic geochemistry into a single computer code is in its infancy and as the application of these calculations moves increasingly into the field of environmental contamination, improvements to our predictive ability are inevitable. Sensible use and interpretation are in order. 

The divide between these two end-members can be fuzzy in practice (Figure 5.2). Development of hybrid codes that employ each method on different components of a model has been a great advance in modeling larger-scale systems.37 Termed QM/MM for quantum mechanics/molecular mechanics, this approach will likely enjoy widespread utilization and success in fields such as soil science, environmental chemistry, and geochemistry due to the nature and complexity of reactions in these fields. Furthermore, as computers become more powerful and software becomes more advanced, it becomes feasible to perform molecular simulations using quantum... 

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