Fig. shows the general framing for describing and generating ABn configuration spaces using the example of tetrahedral coordination and two of the five orthonormal angle-changing modes 𝒒 and 𝒑. , introduced an approach for describing the configuration space in the vicinity of a model reference system's geometry and based upon its vibrational normal modes. While this approach is fully general and meets the requirements for which it was devised, this generality includes the possibility that, for some systems (e.g., crowded high coordination numbers), there could be vibrational modes exhibiting both bond-stretching and angle-changing character when expressed in curvilinear internal coordinates. As noted above, an ABn configuration only depends upon interior angles at the A-atom, hence the solution is to construct the model system such that the appropriate vibrational normal modes are fully separable into (i) purely bond-stretching modes and (ii) purely angle-changing modes. Once armed with purely anglechanging vibrational modes, these can be used as an orthonormal basis to span the corresponding ABn stereoisomeric configuration space.