No abstract

Para-halosubstituted thiophenols (X-TPs, where X is Br, Cl, or F) form ordered islands and monolayers on Cu(111) at temperatures as low as 81 K. At incomplete coverages, all X-TPs adsorb with the dehydrogenated thiol group attached to the substrate and the substituted ring inclined toward the surface, as verified experimentally and theoretically. The structure of ordered islands has a pronounced dependence on the nature of the halogen substituent: while unsubstituted TP and pentafluoro-TP molecules do not self-assemble into extended ordered patterns at 81 K, X-TP molecules form a range of different structures which depend both on the size and electronegativity of the substituent, as well as on the coverage.

We have calculated the electronic structure and the vibrational properties of bulk Li in the fcc and bcc structures using large super-cells and an ab initio, non-local pseudopotential approach with a plane-wave expansion. The method is based on the density functional theory with core corrections and local exchange and correlation effects. The calculated phonon dispersion curves for the bcc structure are compared with the neutron scattering data. The difference between the Helmholtz free energies for the bcc and the closed-packed structures, in the harmonic approximation, is found to be small for the temperature range of interest. The zero-point energies for both structures are substantial, while the heat capacity differential displays a switch at around 90 K.