These examples also highlight the difference between Z-matrix and non-hierarchical internal coordinates. In a non-hierarchical definition, the fragments do not move as a whole, since the effect of gradient terms (or how interpolation is carried out), despite taking place in an internal coordinate space, is still local. Internal coordinate increments mainly affect the atoms directly involved in the coordinate being changed. In the case of Z-matrix space, whole molecules (or moieties) will straightforwardly be moved along the reaction. This also hints to how hierarchical coordinates might be a better choice for molecular cluster optimisations.