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Computational study of the surfaces of quasicrystals

English title Computational study of the surfaces of quasicrystals
Applicant Passerone Daniele
Number 116130
Funding scheme Project funding (Div. I-III)
Research institution Departement Moderne Materialien, ihre Oberfläche und Grenzflächen EMPA
Institution of higher education Swiss Federal Laboratories for Materials Science and Technology - EMPA
Main discipline Condensed Matter Physics
Start/End 01.02.2008 - 31.01.2011
Approved amount 130'550.00
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Keywords (10)

Electronic structure theory; Molecular dynamics simulation; Surface diffusion theory; Empirical interaction potentials; Molecular friction; Atomistic simulation; Complex metallic alloys; Density functional theory; Force field development; Surface science

Lay Summary (English)

Lead
Lay summary
Since their discovery in 1984, quasicrystals (QC) have been the object of an interesting experimental and theoretical debate. Whether they can be described as projection of a 6-dimensional perfect crystal (Krajci & Hafner 2003), as an assembly of icosahedral clusters (Abe et al 2004), or as a periodic tiling of overlapping “quasi-unit cells” (Henley et al 2006; Jeong & Steinhardt 1994; Levine & Steinhardt 1984; Steinhardt & Jeong 1996; Steinhardt et al 1998), for sure there are open problems in their electronic structure, structural properties, diffusion and friction properties that remain unsolved. Even more puzzling is the investigation of atomically well defined surfaces, where few experimental and theoretical investigation exist.
The O. Gröning group at EMPA recently investigated the valence electronic structure of QC (Groning et al 2006; Widmer et al 2006) by means of scanning tunneling microscopy and spectroscopy (STM/STS) at low temperatures (5 K). These measures have revealed signatures of a spiky local density of states (LDOS) near the Fermi energy, exhibiting narrow peaks and pseudo-gaps of the order of 50 meV FWHM. This observation reanimates the discussion of the nature of the valence electronic states in aperiodic crystals, where Bloch’s theorem, fundamental to the band picture in periodic crystals, can not be applied. It has to be concluded that still today the exact nature of the valence electronic structure, especially form the experimental point of view, is not well understood. However this understanding is elementary for the understanding of the anomalous physical properties exhibited by QC and by associated complex metallic alloys.
Moreover, structural aspects involving surface free energy, friction, diffusion, surface reconstructions, are still largely non-understood at the theoretical level. This project proposes a novel and complete strategy for the computational attack of QC surfaces. It relies on existing methods for the classical simulation of alloys, and requires a continuous interplay with experimental and high level ab initio data.
Direct link to Lay Summary Last update: 21.02.2013

Responsible applicant and co-applicants

Employees

Name Institute
Gaspari Roberto

Associated projects

Number Title Start Funding scheme
132375 Molecular self-assemblies, their metallic substrates, and quasicrystal surfaces: a computational approach 01.10.2010 Project funding (Div. I-III)
128754 UP-IPAZIA: “UPgrade and full deployment of the Empa/Eawag computational cluster IPAZIA: towards an interdisciplinary on-site resource for computational sciences” 01.04.2010 R'EQUIP

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