Modernizing Geochemical Simulators
FROM EQUILIBRIUM TO DISEQUILIBRIUM
BUILT FOR COMPLEX REACTIVE SYSTEMS
Why Do Geochemical Simulators Use Basis Species
The architecture of virtually every geochemical simulator in use today was shaped by hardware constraints from the 1970s and 80s. That architecture has persisted ever since, even as computing power has grown by many orders of magnitude.
Early simulators were developed under severe hardware constraints. Reducing the number of unknowns and equations was a practical necessity, and the basis-species formulation ws an efficient way to achieve that. It became the standard, and it has remained so - not because it best represents chemistry, but because it was never necessary to change it.
Why Revisit the Formulation Now?
Modern computing removes the constraints that made basis species necessary in the first place. There is no longer a reason to impose a hierarchy on chemical species, treat redox and gas reactions as special cases, or require users to learn software-specific conventions before they can model real chemistry.
Sym8 is built from the ground up on the premise that modern hardware and software development tools make it both possible and worthwhile to leave those legacy architectural constraints behind and model chemistry the way it actually works.
What is Sym8?
Sym8 is built on a framework of elemental mass conservation rather than the basis-species formulation used by traditional geochemical simulators. In the basis-species approach, a subset of species is designated as "master" species, and all other species are expressed as combinations of these masters — a mathematical convenience that made sense under 1970s hardware constraints but introduces an artificial hierarchy into the chemical system.
In Sym8, every dissolved species — aqueous, redox, and gas — participates directly and equally in a single coupled system of equations. No species is designated as primary or secondary, no redox master species is required, and gases are integrated directly into the chemical framework rather than handled as special cases.
The result is a system of equations that reflects the chemistry directly: what goes into the system must be accounted for in every species that contains it, and the mathematics follows naturally from that physical reality rather than from computational shortcuts inherited from an earlier era.
Practical Implications
When the chemical system is formulated around elemental mass conservation, several things follow naturally. Aqueous, redox, gas, and surface species are all treated consistently within the same mathematical framework — there are no proxy species, no artificial hierarchies, and no special cases. Equilibrium and kinetic processes couple directly, because they are part of the same system rather than handled as separate computational events.
The practical consequences for the user are significant. Fewer numerical edge cases arise, and the solver requires fewer control parameters to manage them. Setting up and interpreting simulations demands chemical intuition rather than familiarity with software-specific conventions. The time spent learning the program is minimized, and the time spent doing science is maximized.
Why Sym8?
Conceptual clarity
Chemistry and mathematical structure are represented directly, making model assumptions easier to understand and interpret.
Realistic simulation scenarios
Mineral reactions, evaporation, gas exchange, and mass-transfer processes are simulated as an integrated single chemical system responding to variable environmental conditions.
Intuitive interface design
The modeling workflow and the structure of the software reflects the fundamental scientific formalism.
Predictable numerical behavior
A clearly defined single solution framework produces consistent results across strongly coupled reaction systems.
Focus on the scientific problem
Users spend time defining reaction systems rather than managing layers of modeling conventions.
How Sym8 Works
No basis chemical species
Solute composition is defined directly from chemical elements rather than from a selected set of basis species.
Single chemical system framework
Chemical reactions, solute concentrations, and elemental mass-balance conditions are solved together within a single mathematical system, without separating basis and secondary species.
Integrated kinetic reactions (Sym8.BK)
Kinetic reaction contributions modify elemental mass-balance equations directly within the defined chemical system framework, avoiding secondary correction steps and operator-splitting methods.
Integrated gas, redox, adsorption, and microbial processes
Gas–water equilibrium (Sym8.EQ), air–water gas exchange (Sym8.BK), redox reaction pairs, adsorption and surface complexation, and microbial reactions are all handled within the same chemical system framework.
Strict elemental mass conservation
Evaporation, inflow, and outflow of water (Sym8.BK) are treated as elemental mass-balance conditions at each timestep rather than as external adjustments to the chemical system framework.
Petrophysical response to water chemistry (Sym8.BK)
Mineralogical composition and reactive surface areas evolve dynamically as water composition changes.
Relational thermodynamic database
Chemical species, reactions, thermodynamic data, and related chemical and physical properties are organized within a relational database rather than distributed text files, allowing centralized management and access.
