The idea behind the RMSD-PP method is to add a Gaussian biasing potential "pushing" the molecule away from the reactant structure and a Gaussian biasing potential "pulling" the molecule towards the product structure. A geometry optimization should (provided that good parameters for sizes and widths of the biasing potentials are used) take the reactant structure to the product structure along the minimum energy path. The path is further refined by 2-4 optimization steps without any bias at every point on the path.