A complete description of tunnelling using direct quantum dynamics simulation: Salicylaldimine proton transfer.

We demonstrate here conclusively that the variational multiconfiguration Gaussian (vMCG) method converges to the grid based full quantum dynamics multiconfiguration time-dependent Hartree result for a tunnelling problem in many dimensions, using the intramolecular proton transfer in salicylaldimine as a model system. The 13-dimensional model potential energy surface was obtained from Hartree Fock energies with the 6-31G* basis set and the expectation value of the flux operator along the transition mode was used as a benchmark characteristic. As well as showing excellent convergence of the vMCG method on the model surface using a local harmonic approximation and a moderate number of basis functions, we show that the direct dynamics version of the vMCG also performs very well, usually needs the same number of Gaussians to converge, and converges to exact results if those are obtained on an accurately fitted surface.

A straightforward method of analysis for direct quantum dynamics: application to the photochemistry of a model cyanine.

We present a new way of analyzing direct quantum dynamics simulations based on a Mulliken-type population analysis. This provides a straightforward interpretation of the wavepacket in much the same way as semiclassical trajectories are usually analyzed. The result can be seen as a coupled set of quantum trajectories.

The geometry and electronic topology of higher-order charged Möbius annulenes.

Higher-order aromatic charged Möbius-type annulenes have been L(k) realized computationally. These charged species are based on strips with more than one electronic half-twist, as defined by their linking numbers. The B3LYP/6-311+G(d,p) optimized structures and properties of annulene rings with such multiple half-twists (C(12)H(12)(2+), C(12)H(12)(2-), C(14)H(14), C(18)H(18)(2+), C(18)H(18)(2-), C(21)H(21)(+), C(24)H(24)(2-), C(28)H(28)(2+), and C(28)H(28)(2-)) have the nearly equal C-C bond lengths, small dihedral angles around the circuits, stabilization energies, and nucleus-independent chemical shift values associated with aromaticity.

A computational investigation of the structure of polythiocyanogen.

Although polythiocyanogen (SCN)(x), has been known for a long time, its solid state structure continues to be uncertain and controversial. Reported here are density functional calculations for linear polymers comprising repeating 1,2,4-dithiazole or 1,2,4-thiadiazole rings, an S-S bridged isomer, and a variety of cyclic phyrin-like systems resulting from cyclization of these linear polymers. The computed energies and comparison of GIAO-derived relative magnetic shieldings for the (13)C and (15)N nuclei with experimental values reported by Woollins and co-workers confirms their assignment of the polymer as based on the 1,2,4-dithiazole ring.

Chiral Aromaticities. A Topological Exploration of Möbius Homoaromaticity.

A series of C2-symmetric homoderivatives of the cyclo C9H9(+) cation first identified by Schleyer as Möbius aromatic are shown to themselves sustain Möbius 4n-π-electron homoaromaticity. Analogous double-twist Möbius bis-homoaromatics follow a 4n+2 electron rule. AIM (atoms-in-molecules) and ELF (electron localization function) analysis of the electron topology in the region of the homobond of these systems reveals that the presence of a AIM bond-critical point in this region is not mandatory, it being unstable to subtle variations in the local electron density induced by local or remote substituents, and which can in turn induce self-annihilation or creation of a pair of bond and ring critical points.

Chiral aromaticities. AIM and ELF critical point and NICS magnetic analyses of Mobius-type aromaticity and homoaromaticity in lemniscular annulenes and hexaphyrins.

An atoms-in-molecules (AIM) and electron localization function (ELF) critical point analysis is reported for two types of lemniscular system, each of which exhibits double-half-twist Mobius topology. This reveals that this type of conformation for [14]annulene 1 has, in addition to the obvious bond critical points (BCPs), two weaker transannular points in the central cross-over region. These can be interpreted in terms of local rings showing single-half-twist Mobius homoaromaticity in addition to the double-half-twist aromaticity revealed by the annulene as a whole.