Exploring the competition between localization and delocalization of the neutral soliton defect in polyenyl chains with the orbital optimized second order opposite spin method.

Theory and implementation of the analytical nuclear gradient is presented for orbital optimized scaled opposite-spin perturbation theory (O2). Evaluation of the O2 analytical gradient scales with the 4th power of molecular size, like the O2 energy. Since the O2 method permits optimization of the orbitals in the presence of wavefunction-based electron correlation, it is suitable for problems where correlation effects determine the competition between localization and delocalization of an odd electron, or hole.

On the nature of electron correlation in C60.

The ground state restricted Hartree Fock (RHF) wave function of C(60) is found to be unstable with respect to spin symmetry breaking, and further minimization leads to a significantly spin contaminated unrestricted Hartree Fock (UHF) solution ( = 7.5, 9.6 for singlet and triplet, respectively).

Characterization of electronically excited states in anionic acetonitrile clusters.

We have identified and examined the excited state of the cluster-solvated, valence-bound acetonitrile anion dimer, consistent with recent experimental findings, determining that the cluster excited state is of predominantly single-excitation character. Potential energy surface scans in coordinates specific to a "dissociative" normal mode common between the excited and ground states of the valence anion as well as the ground-state neutral dimer species shed light on the proposed vibrational autodetachment mechanism, with calculated excited-state lifetime consistent with experiment.

Effects of ligands and spin-polarization on the preferred conformation of distannynes.

Recent experimental and theoretical evidence has shown that distannynes, RSnSnR, can adopt either a singly bonded or a multiply bonded structure. Within calculations on small models, such as MeSnSnMe, apparently dramatic differences in conformational preference have been reported. We show that these differences arise due to the treatment of spin-polarization in density functional theory (DFT), and review stability analysis; a diagnostic for the need to include spin-polarization.

Tunneling through weak interactions: comparison of through-space-, H-bond-, and through-bond-mediated tunneling.

Results from ab initio electronic structure theory calculations on model systems allow for the detailed comparison of tunneling through covalently bonded contacts, hydrogen bonds, and van der Waals contacts. Considerable geometrical sensitivity as well as an exponential distance dependence of the tunneling is observed for tunneling through various nonbonded contacts. However, the fundamental result from the present study is that at most a modest difference is observed between tunneling mediated by H-bonds and tunneling mediated by van der Waals contacts at typical distances for each type of interaction.