Potential energy surface exploration with equilibrial paths. Part I: Theory

The equilibrial path concept is further developed. Special attention is spe nt the symmetry conservation along equilibrial paths and symmetry-breaking. Symmetry-breaking can occur only at singular points. The simple singular p oints of an equilibrial path are valley-ridge inflection points. In contras t to the intrinsic reaction paths and the gradient extremal paths, the equi librial paths enable to describe the branching of reaction channels.