Doubt regarding value of m, m0 and integration methods

[Arindam Basu]

Hello ,
I have a very basic doubt regarding the value of m and m0 while writing the kinetics script of some mineral. I understand that at the beginning of reaction the value of m and m0 are supposed to be same and as reaction proceeds m changes. So I was thinking if we put different m and m0 values in kinetics will that signify something geochemically? I mean can there be any scenario where m and m0 will be different at the beginning of reaction?
Also I have another doubt regarding integration method. So if we are running the simulation for longer periods of time. lets say in thousands of years or million years which method among RK and cvode would you recommend?

[dlparkhurst]

Often the factor (M/M0)^n is used to adjust the surface area of a kinetically-reacting mineral. Usually, M <= M0, which represents the decrease in surface area as the mineral is consumed. If this is the case, then you could start a calculation with M equal to some fraction of M0 and the surface area would be calculated accordingly.

If RK works, then use it; it should be faster than CVODE. However, CVODE is usually the more robust integrator and should work better for some reaction networks, especially "stiff" systems of equations (sets of equations with widely different rates). For long integrations, try to transfer any fast-reacting minerals that react at equilibrium, like carbonates or sulfates, to EQUILIBRIUM_PHASES rather than KINETICS.

[Arindam Basu]

Thank you for your valuable response. This will surely help me in my study