Thanks. However, the problem is not the complexity of the reaction. The problem is that I want to run my simulation about 100 to 200 times for different combinations of reactions' activation energies and pre-exponential factors.  Doing that manually would be a hassle. I was thinking if somehow I could make them the parameters and using DesignXplorer DOE automate the process. In that case, I thought that may be, the rp-var command might help, but got the error (as in my first comment).