Hello. Gwyddion documentation shows that you can do only very basic curve fitting analysis by default http://gwyddion.net/documentation/user-guide-en/graph-processing.html . Of cause you can write your own script for Gwyddion, but I think it would be much easier to export raw data into Matlab (export as .txt and import into Matlab) and use already available scripts written by the community members. In my case (.ibw) Gwiddion does not recognize force-distance curves as curves, instead it plots a weird topography image.