Inclusion Of Tunneling Effects Research Articles

How Fast Do Microhydrated Al Clusters React: A Theoretical Study

The dynamics of the first step of the reaction of small Alm clusters m = {3,13} with up to four water molecules has been studied. The first stage in the reaction, which may ultimately result in the production of H2, is the generation of a HAlmOH·(H2O)n−1 species, which can take place through transition states of the relay type, in which the water molecules may play different catalytic roles; namely, they can be involved directly in a Grotthuss-like mechanism by forming a relay bridge, or they may lower the saddle point energy by interacting with the molecules of the relay bridge. Rate coefficients have been computed with the inclusion of tunneling effects. The results indicate that the optimal configuration (the one giving the highest values of the rate coefficient for 50 K < T < 500 K) in the case of the Al3·(H2O)n system involves three water molecules in the relay bridge. In the case of the Al13 cluster, the two-water system is the most efficient. It is remarkable that Al3 delivers much higher rates tha...

Order–disorder phase boundary between ice VII and VIII obtained by first principles

We report fundamental progress in the description of an archetypical hydrogen-bonded system: H 2 O –ice. We calculated by first principles the ice VII–VIII phase boundary, an order–disorder phase boundary, by performing a complete sampling of configurations in a 16-molecule supercell. Vibrational effects are included within quasiharmonic theory. Several important features were successfully described: negative Clapeyron slope, isotope effect, and nearly-constant T c at low pressures. The equation of state was very well described below 40 GPa. Inclusion of tunneling effects and increase of supercell size should decrease the remaining discrepancies, i.e., the overestimation of volume above ∼40 GPa and the underestimation of T c .

INVERSE DIELECTRIC FUNCTION AND FAST ELECTRON ENERGY-LOSS-SPECTRUM OF SEMICONDUCTOR SUPERLATTICES

The inverse dielectric function of semiconductor superlattices is derived with inclusion of tunneling effects between adjacent quantum wells. The result is, then, used to evaluate the fast electron energy-loss-spotrum with the conclusion that tunneling effect tend to enhance the energy loss in superlattices.