Regensburg 2010 – wissenschaftliches Programm

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O: Fachverband Oberflächenphysik

O 24: Particles and clusters

O 24.7: Vortrag

Dienstag, 23. März 2010, 12:00–12:15, H34

Structural metastability of endohedral M@Si20 cages:
A first-principles sampling study
Alexander Willand1, •Matthias Gramzow2, Stefan Goedecker1, and Karsten Reuter2,31Univ. Basel (Switzerland) — 2Fritz-Haber-Institut Berlin (Germany) — 3Technische Universität München (Germany)

Cage-like clusters are considered as appealing building units for nanoscale materials. Their hollow structure facilitates the incorporation of guest atoms, which can either be viewed as an atomic-scale tailoring of the materials properties of the cage through doping or as a perfect shielding of the encapsulated moiety. With Si in general favoring tetrahedral sp3-coordination, corresponding endohedral metal doping appears as a primary avenue to accomplish the stabilization of Si cage geometries at all. C20 is the smallest known fullerene cage and Si20 cages are building blocks of clathrate materials. We therefore investigate the structural stability of endohedral Si20 structures for a large variety of metal dopants. For this purpose we combine global optimization within minima hopping [1] with a DFT potential energy surface using different levels of xc approximation (LDA, GGA, hybrid functionals). In contrast to previous work proposing endohedral M@Si20 cages as ground state (e.g. [2]) we find for all investigated systems largely more stable isomers, in which the cage structure is broken into smaller cages with additional surface atoms or into completely exohedral isomers. [1] S. Goedecker, JCP 120, 9911 (2004) [2] Q. Sun et al., PRB 65, 235417 (2002).

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