Quasi-classical trajectory (QCT) calculations have been carried out to study the stereodynamics of the reactions H + LiH(+) (v = 0, j = 0) --> H(2) + Li(+) and H(+) + LiH (v = 0, j = 0) --> H(2)(+) + Li which proceed on the two lowest-lying electronic states of the LiH(2)(+) system, using the ab initio potential energy surfaces (PESs) of Martinazzo et al. [J. Chem. Phys., 2003, 119, 11241]. Differential cross sections (DCSs) and alignments of the product rotational angular momentum for the two reactions are reported. Though the two PESs employed in the current calculations have significant differences, the tendencies of the product rotational alignment are same on the whole, and some common features emerge. This interesting phenomenon probably indicates that, for this system, the characters of the PESs have a weak influence on the alignments of the products. The conclusion is confirmed by a further discussion of rotational alignment parameter which also indicates that the two PESs are repulsive, i.e., the exoergic processes of the reactions taking place on the exit valleys of the PESs.

Quasi-classical trajectory calculations have been performed on the adiabatically allowed reactions taking place on the two lowest-lying electronic states of the LiH 2 + system, using the ab initio understanding of the lithium chemistry in the early universe. Thermal rate constants for the above reactions have been computed in the temperature range 10-5000 K and found in reasonably good agreement with estimates based on the capture model.

Transition states and reaction paths for a hydrogen molecule dissociating on small aluminum clusters have been calculated using density functional theory. The two lowest spin states have been taken into account for all the Al(n) clusters considered, with n=2-6. The aluminum dimer, which shows a (3)Π(u) electronic ground state, has also been studied at the coupled cluster and configuration interaction level for comparison and to check the accuracy of single determinant calculations in this special case, where two degenerate configurations should be taken into account. The calculated reaction barriers give an explanation of the experimentally observed reactivity of hydrogen on Al clusters of different size [Cox et al., J. Chem. Phys. 84, 4651 (1986)] and reproduce the high observed reactivity of the Al(6) cluster. The electronic structure of the Al(n)-H(2) systems was also systematically investigated in order to determine the role played by interactions of specific molecular orbitals for different nuclear arrangements. Singlet Al(n) clusters (with n even) exhibit the lowest barriers to H(2) dissociation because their highest doubly occupied molecular orbitals allow for a more favorable interaction with the antibonding σ(u) molecular orbital of H(2).

The isotopic effects on stereodynamic properties for the title reactions occurring on the two lowest-lying electronic potential energy surfaces (PESs) of LiH(2)(+) are investigated in detail by means of the quasi-classical trajectory (QCT) method at a collision energy of 0.5 eV, using the ab initio potential energy surfaces (PESs) of Martinazzo et al. (J. Chem. Phys., 2003, 119, 11241). The corresponding reactions comprise: (i) H/D/T + LiH(+) --> HH/HD/HT + Li(+) and H + LiH(+)/LiD(+)/LiT(+) --> HH/HD/HT + Li(+); (ii) H(+)/D(+)/T(+) + LiH --> HH(+)/HD(+)/HT(+) + Li and H(+) + LiH/LiD/LiT --> HH(+)/HD(+)/HT(+) + Li. Differential cross sections (DCSs) and alignments of the product rotational angular momentum for all of these reactions are reported. The results illustrate that the reason for the abnormal behavior of the DCSs for the title reactions reported in the previous work is ascribed to the sensitive role of the projectile atomic mass, and indicate that the long-range interactions play a more important role than the mass factor in ion-molecule reactions. The current topic for this special mass combination system shows some new features of the stereodynamics differing from the previous studies for "typical" mass-combination reactions.

Recent years have witnessed an ever growing interest in theoretically studying chemical processes at surfaces. Apart from the interest in catalysis, electrochemistry, hydrogen economy, green chemistry, atmospheric and interstellar chemistry, theoretical understanding of the molecule-surface chemical bonding and of the microscopic dynamics of adsorption and reaction of adsorbates are of fundamental importance for modeling known processes, understanding new experimental data, predicting new phenomena, controlling reaction pathways. In this work, we review the efforts we have made in the last few years in this exciting field. We first consider the energetics and the structural properties of some adsorbates on metal surfaces, as deduced by converged, first-principles, plane-wave calculations within the slab-supercell approach. These studies comprise water adsorption on Ru(0001), a subject of very intense debate in the past few years, and oxygen adsorption on aluminum, the prototypical example of metal passivation. Next, we address dynamical processes at surfaces with classical and quantum methods. Here the main interest is in hydrogen dynamics on metallic and semi-metallic surfaces, because of its importance for hydrogen storage and interstellar chem- istry. Hydrogen sticking is studied with classical and quasi-classical means, with particular emphasis on the relaxation of hot-atoms following dissociative chemisorption. Hot atoms dynamics on metal surfaces is investigated in the reverse, hydrogen recombination process and compared to Eley-Rideal dynamics. Finally, Eley-Rideal, collision-induced desorption, and adsorbate-induced trapping are studied quantum mechanically on a graphite surface, and unexpected quantum effects are observed.

The study of molecular species suitable as sensitizers in solar cells involves the understanding of their visible absorption spectrum. In this article we present a detailed theoretical study of the visible band which has been observed for cyanidin in acid solution. We performed accurate DFT and MRPT2 calculations on the protonated cyanidin in vacuo and in solution, where we have also computed the lineshape profile by including the effects of nuclear degrees of freedom in the harmonic approximation.

The ab initio calculation of the interaction forces between the LiH+ molecular ion, at its equilibrium geometry, and several He atoms is carried out in order to isolate and assess the importance of many-body contributions in the search for realistic energy and geometry data. The full potential energy surface (PES) with a single helium partner is obtained first by using an aug-cc-pVQZ basis set for He and higher quality ones for Li and H. The calculations were performed at the CAS-SCF plus MRCI level for the lowest potential energy surface over a total of 480 grid points of the two intermolecular Jacobi coordinates, whereas the excited state surface has also been examined in order to exclude the presence of any significant nonadiabatic interaction between the two PESs. A numerical fit of the lower surface is presented and the general physical changes of the ionic interaction when going from the lower to the upper of the two potentials are described and discussed. The fairly limited importance of many-body effects for such systems is seen from further ab initio calculations including several He atoms: our results suggest that, at least in the present case, no strong charge migration occurs after He attachment, and therefore, one could realistically model larger clusters by implementing a sum-of-potentials approach via the presently computed PES.

The 50 nm-thick polystyrene (PS) film, involved in some innovative memory devices, contains 8-hydroxyquinoline (8HQ) molecules and gold nanoparticles. A model where molecular localized properties directly reflect on macroscopic behavior of a complex system has been tested in the present work, which is focused on the structural and electronic properties of the 8HQ-PS mixture modeled in a continuum scheme: one 8HQ molecule with a polarizable continuum model (PCM) whose reliability has been checked by comparison with periodic DFT calculations of 8HQ-PS crystalline structures. A comprehensive study of the keto-enolic tautomerization of 8HQ has been performed, at the DFT level using B3LYP, LC-PBE, and M052X functionals and a polarized double-ζ basis set. The energetics of the obtained structures (minima and transition states) have been refined by single point calculations at the CCSD(T) level with the aug-cc-pVDZ basis set. Our calculations predict the enolic tautomer to be the most stable for the isolated and PS-solvated 8HQ in its neutral form, with a tautomerization barrier much larger than the thermal energy at the working conditions. The opposite trend has been found for the charged (both positive and negative) 8HQ, with ketonic tautomers being the most stable. In a first approximation of weak interaction with the aluminum electrodes, the electricfield effects have also been taken into account for the calculations of electron affinities and ionization potentials of 8HQ molecules. The electron and hole injection barriers issuing from these results are in good agreement with the experimental observations.