Search results for "tetrahedron"

Nature of the asymmetry in the hydrogen-bond networks of hexagonal ice and liquid water.

2014

The interpretation of the X-ray spectra of water as evidence for its asymmetric structure has challenged the traditional nearly tetrahedral model and initiated an intense debate about the order and symmetry of the hydrogen-bond network in water. Here, we present new insights into the nature of local interactions in ice and liquid water obtained using a first-principle energy decomposition method. A comparative analysis shows that the majority of molecules in liquid water in our simulation exhibit hydrogen-bonding energy patterns similar to those in ice and retain the four-fold coordination with only moderately distorted tetrahedral configurations. Although this result indicates that the tra…

An {Fe60} tetrahedral cage: building nanoscopic molecular assemblies through cyanometallate and alkoxo linkers

2016

International audience; A nanoscopic {Fe60} coordination cage (approximately 3 nm) was prepared by the self assembly of a partially blocked tricyanidoferrate(III) complex and tris(alkoxo)-based iron(III) coordination motifs. This cage is a rare example of a mixed cyanido/alkoxo-bridged high nuclearity complex and it exemplifies the great potential of this new synthetic route to generate uncommon molecular architectures using cyanometallates as metalloligands versus alkoxo-based polynuclear entities.

Binary alloys of Ge and Te: order, voids, and the eutectic composition

2008

The liquid and amorphous structures of ${\mathrm{Ge}}_{0.15}{\mathrm{Te}}_{0.85}$ and GeTe alloys are characterized using combined density functional/molecular dynamics simulations. Te is threefold coordinated, in contrast with predictions of the ``8-$N$ rule,'' and Ge atoms (fourfold coordinated) show octahedral and tetrahedral bonding angles. Cubic local environment occurs in both materials, and GeTe shows a pronounced alternation of atomic types. Tetrahedral Ge coordination is more common in the eutectic ${\mathrm{Ge}}_{0.15}{\mathrm{Te}}_{0.85}$, which comprises corner- and edge-sharing ${\mathrm{GeTe}}_{4}$ units surrounded by Te. There is no Te segregation, and the material resembles …

Enhanced light confinement in a triangular aperture: Experimental evidence and numerical calculations

2005

We have recently demonstrated that the electric near-field emerging from a triangular aperture at the tip of a metal-coated tetrahedron of glass exhibits a highly confined and intense spot when the light incident from within the glass body is polarized perpendicularly to one edge of the aperture [Naber et al., Phys. Rev. Lett. 89, 210801 (2002)]. Here we present additional experimental material and a theoretical confirmation of this near-field optical effect. Based on the model of a triangular aperture in a planar metal film, we studied the influence of aperture size and film material on the field distribution. Even though our theoretical model is rather simplified as compared to the experi…

Amorphous silica between confining walls and under shear: a computer simulation study

2002

Molecular dynamics computer simulations are used to investigate a silica melt confined between walls at equilibrium and in a steady-state Poisseuille flow. The walls consist of point particles forming a rigid face-centered cubic lattice and the interaction of the walls with the melt atoms is modelled such that the wall particles have only a weak bonding to those in the melt, i.e. much weaker than the covalent bonding of a Si-O unit. We observe a pronounced layering of the melt near the walls. This layering, as seen in the total density profile, has a very irregular character which can be attributed to a preferred orientational ordering of SiO4 tetrahedra near the wall. On intermediate lengt…

Interplay Between Spin-Orbit Coupling and Structural Deformations in Heavy Transition-Metal Oxides with Tetrahedral Coordination

2018

Extended x-ray absorption fine structure spectroscopy and first-principles study of SnWO4

2014

The local atomic structure in α- and β-SnWO 4 was studied bysynchrotron radiation W L 3 -edge X-ray absorption spectroscopy at 10 and 300 K.Strongly distorted WO 6 octahedra were found in α-SnWO 4 , whereas nearly regularWO 4 tetrahedra were observed in β-SnWO 4 , confirming previous results. Thestructural results obtained were supported by the first-principles calculations,suggesting that the second-order Jahn-Teller effect is responsible for octahedraldistortion.

Inverse simulated annealing: Improvements and application to amorphous InSb

2014

An improved inverse simulated annealing method is presented to determine the structure of complex disordered systems from first principles in agreement with available experimental data or desired predetermined target properties. The effectiveness of this method is demonstrated by revisiting the structure of amorphous InSb. The resulting network is mostly tetrahedral and in excellent agreement with available experimental data.

Prehnite: Structural similarity of the monoclinic and orthorhombic polymorphs and their Si/Al ordering

1990

Abstract Two modifications of the naturally occurring mineral prehnite, Ca 2 Al(Si 3 AlO 10 )(OH) 2 , are characterized by precise single crystal diffraction methods. The two forms are topologically identical. They differ only in the siting of one Al and one Si atom per unit cell: these switch their places in two of the tetrahedrally coordinated sites. This appears to be the only known case where a silicate occurs with two differently ordered tetrahedral distributions of Al and Si atoms. The two forms are not polytypes according to the current definition of polytypes. The two modifications are so similar to each other that they differ only in the eighth coordination sphere.

Hydrogen and deuterium decoration of In-vacancy complexes in nickel.

1987

The quantum-mechanical states of hydrogen and deuterium in pure and defected nickel have been calculated using the effective-medium theory. The defects considered include monovacancies, the substitutional In impurity, a complex of four vacancies, and a complex of an In impurity decorated with a tetrahedron of four vacancies. While the substitutional In impurity does not trap hydrogen, the vacancy and the vacancy complexes with and without In association do. The calculated binding energy to the four vacancy complex is nearly insensitive to the hydrogen isotopic mass and to the In decoration. These results, along with the dependence of the hydrogen binding energy on multiple hydrogen occupanc…