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Abstract: The bonding and energetics in H(S2N2) Y H are analyzed within two models of conductivity. The effective exchange and mixed-valence models for conductivity predict similar geometric changes. The effects of hydrogen capping on the geometries were removed by averaging the central bond lengths and angles in the larger oligomers. The extrapolated singlet–triplet energy gap, predicted to be between 2.44 and −2.54kcalmol−1 for the polymer, accounts for conductivity along the chain axis, the suppression of a Peierls instability and the failure to synthesize single strand (SN) X . Extrapolated values for the ionization potential, between 5.61 and 5.17eV, electron affinity, between 3.40 and 4.08eV, and disproportionation energy, between 2.14 and 0.98eV, are consistent with previous estimates. The perpendicular conductivity can be related to the small, but non-negligible, disproportionation energy. An analysis of the charge distributions reveal that both models of conductivity have a common electron-phonon mechanism, suggesting that the remarkable superconductivity in (SN) X is best explained as a combination of the effective exchange and mixed-valence modes of conductivity. [Copyright &y& Elsevier]

The nature of the stationary point of oxirene, cyclic C2H2O, has been examined using selected GGA and hybrid functionals in combination with a number of basis sets. All GGA functionals (BLYP, BP91, PBE, HCTH, HCTH147, and HCTH407) predict the stationary point to be a transition state and show very little basis set dependence. The hybrid functionals (B3LYP, B3P91, PBE0, B97, B97-1, and B3P86), on the other hand, show more basis set dependence and predict oxirene to be a minimum in a number of cases. However, these parameterized hybrid functionals are not consistent in their characterization of oxirene. The theoretically derived hybrid functional PBE0 predicts oxirene to be a minimum with 11 of the 12 basis sets used and results with the largest basis set are in good agreement with earlier predictions with the high level correlated method, CCSD(T). [Copyright &y& Elsevier]