The electronic structure at organic/organic interfaces plays a key role, among others, in defining the quantum efficiency of organics-based photovoltaic cells. Here, we perform quantum-chemical and microelectrostatic calculations on molecular aggregates of various sizes and shapes to characterize the interfacial dipole moment at pentacene/C 60 heterojunctions. The results show that the interfacial dipole mostly originates in polarization effects due to the asymmetry in the multipolar expansion of the electronic density distribution between the interacting molecules, rather than in a charge transfer from donor to acceptor. The local dipole is found to fluctuate in sign and magnitude over the interface and appears as a sensitive probe of the relative arrangements of the pentacene and C 60 molecules (and of the resulting local electrical fields sensed by the molecular units).

A semiempirical quantum-chemical model based on a fragment orbital formalism is presented to assess molecular parameters relevant to charge transport in organic crystals. The mixed valence bond/Hartree-Fock approach provides an efficient integrated framework to evaluate the electronic polarization effects induced by localized charge carriers and the associated impact on the matrix elements mediating electron migration in the hopping regime. This formalism, applied here to anthracene clusters of increasing sizes and dimensionalities, yields the electrostatic and polarization contributions to the total interaction energy of the neutral and charged aggregates and leads to a reduction in the effective bandwidth by ϳ10% -20% as a result of the polarization cloud.

Normal incidence scattering of hydrogen atoms off a H-covered tungsten W(110) surface is simulated via quasiclassical trajectories. A density functional theory (DFT) based multiadsorbate potential is developed to model a wide range of surface coverages, θ = 0.25−1 monolayer (ML), reproducing the surface arrangements observed at low temperature. The competition between hot-atom (HA) and Eley−Rideal (ER) abstraction mechanisms is studied for collision energies of the projectile atom in the range E p = 0.1− 5.0 eV (E p = 0.1−2.0 eV) for θ = 0.25 ML (θ = 0.5, 0.75, and 1 ML) coverage. Cross sections, final energies of the recombination products, and reaction times are analyzed. At low coverage and low collision energy, HA dominates the abstraction, whereas HA and ER cross-sections become similar when collision energy increases. The vibrational distribution of recombined H 2 molecules at finite coverage is found to be in better agreement with experiments than the one computed within the single adsorbate limit. At high surface coverage, ER dominates abstraction but the dynamical observables highlight the similarity between both reaction mechanisms, thus suggesting that abstraction may be considered as a unique process.