We now turn our attention to a multi-dimensional system. Water is an attractive system to benchmark against, as water only has three internal degrees of freedom which makes it possible to easily describe the PES in the full coupling limit and also carry out the dynamics at the full coupling level. The three internal degrees of freedom are described using normal coordinates and we enumerate the normal coordinates as q 0 , q 1 , and q 2 for the symmetric bend, symmetric stretch, and asymmetric stretch, respectively.