Perturbational analysis of the topological effect on molecular-orbital energies

The newly established topological-effect-on-molecular-orbitals (TEMO) theorem has been subjected to a detailed perturbational analysis; this is done in a novel manner by means of the powerful perturbational-variational Rayleigh-Ritz (PV-RR) procedure. TEMO predicts relationships between the molecular-orbital (MO) energy patterns of topologically related $\mathcal{S}$ and $\mathcal{T}$ molecular isomers. The surprisingly strong effect of pure topological factors on the physics of the molecules is demonstrated by the excellent agreement between TEMO predictions and nonempirical self-consistent-field MO calculations. Application of the PV-RR procedure in conjunction with recently introduced radius-of-convergence considerations enables us to dissect in fine detail the influence of perturbations on the TEMO patterns, and thus, for the first time, to study quantitatively the relationship between the topological and physical factors in molecular calculations.