We have investigated adsorption of a single H atom onto a charge-neutral B&2H» cluster, which simulates one of the subunits of an icosahedral boride. Five different paths of approach are considered for the H atom. At the level of fourth-order Moiler-Plesset perturbation theory, only one of these paths leads to an equilibrium position in which the adsorption energy is positive. Although H can pass inside the icosahedral B» cage, the most stable position is outside the cage, corresponding approximately to the position for which electronic charge transfer to the 8» cage is a maximum. A comparison is carried out between the charge densities and one-electron energy levels of the cluster in the absence and presence of the adsorbate.

No abstract

No abstract

There is evidence that solitons are created by doping in certain of the quarter-filled-band semiconducting molecular crystals having large Coulomb repulsion for two electrons on the same site-("large U"). Since, as has been shown for polyacetylene, soliton concentrations depend on the concentrations of band carriers, it is necessary to know the chemical potentials of the solitons to find the electronic Fermi energy. We derive in this work the relations between soliton chemical potentials and the Fermi energy for quarter-filled-band, large-U semiconductors and use them to find concentrations of solitons, electrons, and holes as a function of temperature and chemical doping. Numerical results are presented for parameters appropriate to (N-methylphenazinium)"(phenazine)& "tetracyanoquinoditnethanide [(NMP)"(Phen)i "TCNQ] for x =0.50 (exactly quarter-filled band) and x =0.54 (4% donor doping). The Fermi energy is found to be twice the chemical potential of the negatively charged solitons. For doped systems, the Fermi energy decreases approximately linearly with temperature at low temperatures, with a slope depending on the level of doping. At low temperatures we find also that the number of solitons we'll be less than twice the number of dopant molecules (their number at T =0 K) due to promotion of electrons from soliton levels to the conduction band and subsequent soliton recombination.