Gamry’s EIS Analysis features a simple-to-use automatic EIS model-fitting routine. It is based on the well-known Simplex non-linear least-squares fitting routine.
Unlike older fit routines, it does not depend on user-entered seed values for a model’s parameters. It automatically chooses seed values prior to a traditional Simplex curve fit.
Gain access to Autofit from the Echem Analyst™ menu by selecting Impedance, Fit a Model (Simplex method). This opens a dialog box somewhat like this:
As you would in other EIS fit routines, you can enter values (seed values) for the model’s parameters and click the Calculate button to find the values of the model parameters that most closely match the measured EIS spectrum. As in other fit routines, poor seed values can cause lack of convergence in the fit or a less than optimal fit. Alternatively, you can ignore the seed values and click the AutoFit button. The seed values are determined in a proprietary manner, and these seed values are then used to fit the model. Experience has shown this method to be effective on models with as many as eighteen adjustable parameters.