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Xenon, which is quite inert under ambient conditions, may become reactive under pressure. The possibility of the formation of stable xenon oxides and silicates in the interior of the Earth could explain the atmospheric missing xenon paradox. Using an ab initio evolutionary algorithm, we predict the existence of thermodynamically stable Xe-O compounds at high pressures (XeO, XeO2 and XeO3 become stable at pressures above 83, 102 and 114 GPa, respectively). Our calculations indicate large charge transfer in these oxides, suggesting that large electronegativity difference and high pressure are the key factors favouring the formation of xenon compounds. However, xenon compounds cannot exist in the Earth's mantle: xenon oxides are unstable in equilibrium with the metallic iron occurring in the lower mantle, and xenon silicates are predicted to decompose spontaneously at all mantle pressures (<136 GPa). However, it is possible that xenon atoms may be retained at defects in mantle silicates and oxides. [ABSTRACT FROM AUTHOR]

Quantum-mechanical molecular dynamics have been used to investigate structural and physical properties of the 1/1 approximant of the icosahedral Al-Cu-Fe quasicrystal. Particular local structural arrangements of atoms, referred to here as clusters, have been analyzed with respect to their properties within the crystal structure. Artificial strain and cracks have been introduced to probe their mechanical properties, and artificial surfaces have been created to investigate their role for surface termination. From the energetics of the ab initio calculations results that flat surfaces cutting clusters are favored over puckered surfaces keeping clusters intact. The Vienna Ab-initio Simulation Package (vasp) was used for all calculations. [ABSTRACT FROM AUTHOR]

The article presents a study on the building principle of complex centered cubic intermetallic structures. It explores the periodic and quasiperiodic crystallography of complex intermetallics. It states that complex intermetallics follow uniform building principles regardless of their chemical compositions and bonding. It also notes intermetallic compounds are prone to develop giant unit cells if their stoichiometry favors three-dimensional atomic clusters.

This is the second of two papers, where we discuss the cluster structures of a novel family of cluster-based intermetallic phases of unprecedented complexity: cF444-Al6.36Ta36.4 (AT- 19), a = 19.1663 (1) Å, V = 7040 ų, cF(5928 - x)- Al56.6Cu3.9Ta3.95, x = 20 (ACT-45), a = 45.376 (1) Å, V = 93 428 ų and cF(23, 256 - x)-Al55.4Cu5.4Ta3.91, x = 122 (ACT- 71), a = 71.490 (4) Å, V= 365 372 ų. The space group is F4¯3m in all three cases. The structures can be described as packings of clusters such as fullerenes, dodecahedra, pentagonal bifrusta and Friauf polyhedra. A characteristic feature of the two larger structures are nets of hexagonal bipyramidal Ta clusters (h.b.p.). The extremely short distance of 2.536-2.562 Å between their apical Ta atoms indicates unusually strong bonding. The large h.b.p. nets are sandwiched between slabs of Friauf polyhedra resembling the structure of the μ phase. [ABSTRACT FROM AUTHOR]