To model the bond breaking in the molecules, the most native coordinate is the distance between the atoms: R i j = (r i -r j ) 2 , where i and j are the atomic indexes, and r i , r j denote atomic position vectors. However, since there might be cases when more than two bonds are broken during a reaction, such as the double proton transfer or the breaking of the cycles, we might need more than one distance in the CV definition. Therefore, we will take the following definition of the CV: