Glimmers of Complexity Three-Configuration Solutions

Orbital overlaps for one (any) of the three equivalent all-sigma MCSC configurations (7 bh=2.24 ao). 

The overlap between any two individually-normalized configurations is 0.874. Orbital overlaps are given in Table 5. 

However, it is not invariant under reflection into any of the three ov symmetry planes. It thus does not have the full symmetry required for an A state, and it is only fully symmetric in the C31, subgroup of the D31, molecular point group. The energy lies a further O.lOeV below that of the all-sigma three-configuration solution (see Table 4). 

If these six configurations are used in a non-orthogonal configuration-interaction calculation (VB-CI), the resulting energy is about 0.17 eV lower than that of the symmetry-contaminated three-configuration MCSC wavefunction. 

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