Theoretical positron lifetime values have been calculated systematically for most of the elements of the periodic table. Self-consistent and non-self-consistent schemes have been used for the calculation of the electronic structure in the solid, as well as different parametrizations for the positron enhancement factor and correlation energy. The results obtained have been studied and compared with experimental data, confirming the theoretical trends. As is known, positron lifetimes in bulk show a periodic behaviour with atomic number. These calculations also confirm that monovacancy lifetimes follow the same behaviour. The effects of enhancement factors used in calculations have been commented upon. Finally, we have analysed the effects that f and d electrons have on positron lifetimes.

The appearance of "magic" heights of Pb islands grown on Cu(111) is studied by self-consistent electronic structure calculations. The Cu(111) substrate is modeled with a one-dimensional pseudopotential reproducing the essential features, i.e. the band gap and the work function, of the Cu band structure in the [111] direction. Pb islands are presented as stabilized jellium overlayers. The experimental eigenenergies of the quantum well states confined in the Pb overlayer are well reproduced. The total energy oscillates as a continuous function of the overlayer thickness reflecting the electronic shell structure. The energies for completed Pb monolayers show a modulated oscillatory pattern reminiscent of the super-shell structure of clusters and nanowires. The energy minima correlate remarkably well with the measured most probable heights of Pb islands. The proper modeling of the substrate is crucial to set the quantitative agreement.

All material supplied via Aaltodoc is protected by copyright and other intellectual property rights, and duplication or sale of all or part of any of the repository collections is not permitted, except that material may be duplicated by you for your research use or educational purposes in electronic or print form. You must obtain permission for any other use. Electronic or print copies may not be offered, whether for sale or otherwise to anyone who is not an authorised user.Powered by TCPDF (www.tcpdf.org)Self-consistent study of electron confinement to metallic thin films on solid surfaces We present a method for density-functional modeling of metallic overlayers grown on a support. It offers a useful tool to study nanostructures, combining the power of self-consistent pseudopotential calculations with the simplicity of a one-dimensional approach. The model is illustrated for Pb layers grown on the Cu͑111͒ surface. The analysis provides the strength of the electron confinement barriers in thin slabs with accuracy, supporting the interpretation of the quantum well state spectra measured by scanning tunneling spectroscopy. On the other hand, it offers a benchmark to check the simple analytical models commonly used in the literature to study metallic films on semiconducting or metallic surfaces. As a result, some deficiencies are detected in the applicability of those models, which often lead to an overestimation of the number of wetting layers. Finally, an improved formula is proposed.

The stability of metallic nanowires is studied by analysing the shell- and supershell structures of total energy oscillations. Fully quantum-mechanical calculations are performed for Cs, Na and Al nanowires covering the whole range of valence electron densities in simple metals. Nanowires are modelled as infinite stabilized jellium cylinders and solving for their electronic structure self-consistently. The results are analysed within a semiclassical model. A comparison between the shell structures of nanowires and atomic clusters is made.

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