Rocco Martinazzo

Understanding adsorption of hydrogen atoms on graphene

Adsorption of hydrogen atoms on a single graphite sheet (graphene) has been investigated by first-principles electronic structure means, employing plane-wave based periodic density functional theory. A 5 x 5 surface unit cell has been adopted to study single and multiple adsorptions of H atoms. Binding and barrier energies for sequential sticking have been computed for a number of configurations involving adsorption on top of carbon atoms. We find that binding energies per atom range from approximately 0.8 to approximately 1.9 eV, with barriers to sticking in the range 0.0-0.15 eV. In addition, depending on the number and location of adsorbed hydrogen atoms, we find that magnetic structures may form in which spin density localizes on a square root(3) x square root(3)R30 degrees sublattice and that binding (barrier) energies for sequential adsorption increase (decrease) linearly with the site-integrated magnetization. These results can be rationalized with the help of the valence-bond resonance theory of planar pi conjugated systems and suggest that preferential sticking due to barrierless adsorption is limited to formation of hydrogen pairs.

Symmetry-induced band-gap opening in graphene superlattices

We study

The gas-phase lithium chemistry in the early universe: elementary processes, interaction forces and quantum dynamics

n\ifmmode\times\else\texttimes\fi{}n

Accurate potential energy surfaces for the study of lithium–hydrogen ionic reactions

honeycomb superlattices of defects in graphene. The considered defects are missing

Quantum dynamics of ultrafast charge transfer at an oligothiophene-fullerene heterojunction

{p}_{z}

A local coherent-state approximation to system-bath quantum dynamics

orbitals and can be realized by either introducing C atom vacancies or chemically binding simple atomic species at the given sites. Using symmetry arguments and electronic-structure calculations we show that it is possible to open a band gap without breaking graphene point symmetry. This has the advantage that new Dirac cones appear right close to the gapped region. We find that the induced gaps have an approximate square-root dependence on the defect concentration

Possible reaction paths in the LiH+2 chemistry: a computational analysis of the interaction forces

x=1/{n}^{2}

Hot-atom versus Eley–Rideal dynamics in hydrogen recombination on Ni(100). I. The single-adsorbate case

and compare favorably with those found in nanoribbons at the same length scale.

A modified Variable-Phase algorithm for multichannel scattering with long-range potentials

Abstract In this work we review the efforts made in the last 10 years to understand the neutral and ionic chemistry of LiH. The relevance of most of the studies on this subject is due to the possible importance of the LiH molecules and relative ions in the primordial universe chemistry. Although it is still not clear what could be the role of LiH in the early universe chemistry, since experimentally important data are indeed still missing and its relevance may be limited by the small abundance of Li molecular species that is thought to exist at the recombination era, it is already important from a fundamental point of view to gather the various results obtained up to now since, in our opinion, they are already able to shed light on a large portion of the gas-phase chemistry of LiH and of its positive ion. Most of the results that will be summarized here are theoretical and computational, intending to provide the present state of our knowledge on the relevant potential energy surfaces and dynamical processes which ensue from their features.

Three-dimensional reactive surfaces for the LiH2+ system: an analysis of accurate ab initio results

Three-dimensional potential energy surfaces (PESs) have been computed, and numerically fitted, for the two lowest electronic states of the LiH2+ system, which are of importance for the astrophysically relevant LiH++H→Li++H2 and LiH+H+→Li+H2+ exoergic reactions. We extend the recently computed 11 000 multi reference valence bond ab initio energy values [Martinazzo et al., Chem. Phys. 287, 335 (2003)] with 600 multireference configuration interaction calculations with complete active self-consistent field reference functions and a large Li(12s10p4d1f)/H(8s6p3d1f) basis set. We have fitted the full set of energy values with a modified Aguado–Paniagua ansatz that correctly takes into account in this ionic system the important long-range contributions to the potential. Calibration calculations on the three-body potential term and the use of essentially exact results for the two-body contributions allow us to estimate the overall accuracy of the analytic PESs to be within that required for accurate quantum scat...