The ionic weight against how much ionic structure is in the wavefunction

One of the figures on bonding models: Valence bond, molecular orbital and hybrids, drawn as descriptions of one thing rather than as competing pictures.

Two essays draw this figure, each at the values its own argument needs rather than at the setting shown above. What each one uses it to show is below, in the words of its own caption.

A weight that depends on how it is weighed

The three conventions on two wavefunctions at hydrogen’s bond length. On a wavefunction with a quarter of the molecular orbital picture’s ionic content they disagree by a factor of six; on a purely covalent one, two of them report nothing and the third reports a quarter.

The ionic weight under each convention as the wavefunction is swept from purely covalent to the molecular orbital form. All three meet at the right-hand end, where the wavefunction is symmetric between the two structures and any convention must give fifty per cent. They also meet at nothing in between.

The same weights as the overlap between the structures is raised from zero. At zero the structures are orthogonal, squaring a coefficient is a weight, and all three conventions are that squared coefficient to the last bit a double holds. Everything above is what non-orthogonality does.

The pair that is not a tie

The four predictors under both instruments. The worst case of each is invisible to the other.