Do the VSEPR Points-on-a-Sphere Repulsions Simulate Quantum Interactions?

The Valence-Shell-Electron-Pair-Repulsion theory, in its Points-on-a-Sphere (POS) variant has been heretofore almost exclusively applied to molecular structure. It is shown that the POS model also implies the form of the potential energy surface for · bending deformations of molecules. The extent to which this elementary mechanical model simulates quantum mechanical interactions in binary compounds of main-group elements is investigated using recent EHT molecular orbital calculations to supplement the rather sparse accumulation of experimental and ab initio characterizations of potential surfaces. It is found that the POS force field, in the main, parallels quantum quadratic and anharmonic components so closely that it promises to become a useful tool in spectroscopic and diffraction research. A simple effective force law between repelling points, namely -CJV;i (r)/or ex r-<•+1>, accounts well for the known data<. For experiment and ab initio theory, the parameter s expressing the hardness of repulsions is about 4, while for EHT computations with frozen VOIP values, interactions are slightly harder with s = 6. Implications are briefly discussed.