CONSTRUCTION OF HIGH-SYMMETRY SHEET-LIKE INTRUSIONS IN THE UPPER CRUST THROUGH AMALGAMATION OF LOW-SYMMETRY LOBES

2017 ◽  
Author(s):  
Eric Horsman ◽  
Keyword(s):  
High Symmetry ◽  
Upper Crust ◽  
Low Symmetry

The usefulness of high index low symmetry zone axes for holz line analysis

1987 ◽  
Vol 45 ◽  
pp. 384-385
Author(s):  
C. M. Sung ◽  
D. B. Williams
Keyword(s):  
Lattice Parameter ◽  
High Order ◽  
Zone Axis ◽  
High Index ◽  
High Symmetry ◽  
Second Phases ◽  
Line Patterns ◽  
Low Symmetry ◽  
Line Analysis

Researchers have tended to use high symmetry zone axes (e.g. <111> <114>) for High Order Laue Zone (HOLZ) line analysis since Jones et al reported the origin of HOLZ lines and described some of their applications. But it is not always easy to find HOLZ lines from a specific high symmetry zone axis during microscope operation, especially from second phases on a scale of tens of nanometers. Therefore it would be very convenient if we can use HOLZ lines from low symmetry zone axes and simulate these patterns in order to measure lattice parameter changes through HOLZ line shifts. HOLZ patterns of high index low symmetry zone axes are shown in Fig. 1, which were obtained from pure Al at -186°C using a double tilt cooling holder. Their corresponding simulated HOLZ line patterns are shown along with ten other low symmetry orientations in Fig. 2. The simulations were based upon kinematical diffraction conditions.

An X-ray diffraction study of AgNbO3 and comparison with NaNbO3

1999 ◽  
Vol 14 (4) ◽  
pp. 253-257 ◽  
Author(s):  
C. N. W. Darlington
Keyword(s):  
Diffraction Pattern ◽  
Figure Of Merit ◽  
Parent Phase ◽  
Incident Beam ◽  
Large Error ◽  
High Symmetry ◽  
X Ray Diffraction ◽  
Beam Focusing ◽  
Low Symmetry

The powder diffraction pattern of the perovskite AgNbO3 has been measured using CuKα1 radiation with an incident beam focusing monochromator to eliminate the Kα2 component. Indexing the pattern shows that the multipartite cell is 2×2×4 times that of the pseudocubic subcell. Comparison is made with the diffraction pattern of NaNbO3, which has a similar multipartite unit cell. There are strong similarities, but close inspection shows that the structures are not isomorphous. The paper concludes with a discussion of the figure of merit FN for pseudosymmetric structures. It is suggested that two figures of merit be reported. The first should be the standard one using either all measured reflections or just the first 30. The proposed second figure of merit does not include any superlattice reflections. These superlattice reflections tend to be very weak, resulting in a low completeness factor and relatively large error in the measurement of their position. This effect produces an unrealistically low value of the standard figure of merit. By including only “main” reflections, i.e., those reflections that are common to both the low-symmetry and high-symmetry parent phase (if it exists), a much better estimate of the quality of the fitting of the measured diffraction pattern is obtained.

scholarly journals Nucleus-independent chemical shift profiles along the intrinsic distortion path for Jahn-Teller active molecules. Study on cyclopentadienyl radical and cobaltocene

2015 ◽  
Vol 80 (7) ◽  
pp. 877-888 ◽  
Author(s):  
Ljubica Andjelkovic ◽  
Marko Peric ◽  
Matija Zlatar ◽  
Maja Gruden-Pavlovic
Keyword(s):  
Density Functional ◽  
Chemical Shifts ◽  
High Symmetry ◽  
Functional Theory ◽  
Aromatic Character ◽  
Nucleus Independent Chemical Shift ◽  
Jahn Teller ◽  
Cyclopentadienyl Radical ◽  
Cyclopentadienyl Anion ◽  
Low Symmetry

The aromatic/antiaromatic behavior of the cyclopentadienyl anion (Cp-), bis(?5-cyclopentadienyl)iron(II) (Fe(Cp)2), as well as of the Jahn-Teller (JT) active cyclopentadienyl radical (Cp?) and bis(?5-cyclopentadienyl)cobalt(II) (Co(Cp)2) has been investigated using Density Functional Theory (DFT) calculations of the Nuclear Independent Chemical Shifts (NICS). According to the NICS values, pentagon ring in Fe(Cp)2 is more aromatic than isolated Cp-. The NICS parameters have been scanned along the Intrinsic Distortion Path (IDP) for Cp? and Co(Cp)2 showing antiaromaticity, which decreases with increasing deviation from high symmetry D5h to low symmetry (LS) C2v. Changes in the NICS values along the IDP revealed that Co(Cp)2 in the LS nuclear arrangement has aromatic character, in contrast to the case of Cp?

TIGHT-BINDING MOLECULAR DYNAMICS STUDY OF C60, C116 AND C120

1996 ◽  
Vol 10 (17) ◽  
pp. 831-838
Author(s):  
ZHILIANG CAO ◽  
XUEPING YU ◽  
JIBING XIANG ◽  
PEIZHU DING ◽  
RUSHAN HAN
Keyword(s):  
Molecular Dynamics ◽  
Molecular Simulation ◽  
Ground State ◽  
Tight Binding ◽  
Ground States ◽  
High Symmetry ◽  
Vibrational Modes ◽  
Relative Movement ◽  
Energy Bands ◽  
Low Symmetry

The geometric structures of C 60, C 116 and C 120 in their ground states are obtained by tight-binding dynamic molecular simulation (TBMD). We find that the ground state of C 60 has high symmetry, Ih, but C 116 and C 120 have low symmetry, D2h. The energy bands and vibrational modes of C 116 and C 120 are complex compared with C 60. Some of them can be easily recognized as C 60 derived and are no longer degenerate but very close, and others are produced by the interaction and relative movement between two C 58 or two C 60.

scholarly journals Local Symmetry Breaking in the High Temperature Regime of SnTe

2014 ◽  
Vol 70 (a1) ◽  
pp. C857-C857
Author(s):  
Kevin Knox ◽  
Emil Bozin ◽  
Christos Malliakas ◽  
Mercouri Kanatzidis ◽  
Simon Billinge
Keyword(s):  
High Temperature ◽  
Ground State ◽  
Ferroelectric Phase ◽  
Local Symmetry ◽  
High Symmetry ◽  
Lead Chalcogenides ◽  
Atomic Pair Distribution Function ◽  
Atomic Pair ◽  
Spatial Fluctuations ◽  
Low Symmetry

The term emphanisis [1] has been coined to define the appearance of local off-centering displacements of ions from a high-symmetry ground state on warming, as recently discovered in PbTe [2]. Such a phenomenon is unusual because, in the canonical view of structural transformations, a low-symmetry ground state evolves into a higher symmetry state on warming. Although it is not uncommon for remnants of a low-symmetry phase to appear as spatial fluctuations at high temperature, the emergence of a locally broken symmetry state from a high symmetry ground state is quite rare. Emphanisis may be behind some long-known, but poorly understood anomalies seen in the lead chalcogenides. However, the origin and nature of emphanisis are still the subject of controversy. Several explanations for emphanisis have been suggested, including a simple response to an underlying anharmonic potential [3], a dynamic ferroelectric-like off-centering [2], and a temperature-dependent competition between ionicity and covalency [1], but an understanding remains elusive. In this talk I will report on atomic pair distribution function (PDF) measurements of the lead-free compound SnTe, which is isostructural to PbTe at high T but with a ferroelectric phase below Tc ~ 100K. Our data show that SnTe also exhibits an emphanitic response, but with an onset temperature well above Tc and a symmetry that is distinct from that of the ferroelectric phase. Taken together these results suggests that the emphanitic and ferroelectric responses are quite distinct.

High-resolution image simulations of small metal particles

1991 ◽  
Vol 434 (1891) ◽  
pp. 279-296 ◽  
Keyword(s):  
High Resolution ◽  
Charge Density ◽  
Metal Particles ◽  
High Symmetry ◽  
Resolution Image ◽  
High Resolution Image ◽  
Low Symmetry ◽  
Image Simulations ◽  
Small Metal Particles ◽  
Number Of Particles

The results of extensive multislice simulations of decahedral and icosahedral multiply twinned and face centred cubic (FCC) cuboctahedral particles are presented for a matrix of both high- and low-symmetry orientations. For the high-symmetry axes the image contrast is confirmed as being directly interpretable in term s of the projected charge density of the structure, whereas the lower symmetry orientations give rise to complex contrast. In the case of the FCC based morphology the effects of contrast due to formally forbidden reflections is also investigated. The results of this study have allowed a larger number of particles to be positively identified than has previously been possible and experimental images of particles in both high- and low-symmetry orientations are shown.

The generation of stationary π-electron rotations in chiral aromatic ring molecules possessing non-degenerate excited states

2016 ◽  
Vol 18 (3) ◽  
pp. 1570-1577 ◽  
Author(s):  
Masahiro Yamaki ◽  
Yoshiaki Teranishi ◽  
Hiroki Nakamura ◽  
Sheng Hsien Lin ◽  
Yuichi Fujimura
Keyword(s):  
Angular Momentum ◽  
Aromatic Ring ◽  
Excited States ◽  
High Symmetry ◽  
Laser Fields ◽  
Ring Molecules ◽  
Fundamental Quantity ◽  
Low Symmetry

Stationary angular momentum, which is a fundamental quantity of high-symmetry aromatic ring molecules, can be created for low-symmetry ring molecules by applying theoretically designed stationary laser fields.

Reflection splitting-induced microstrain broadening

2017 ◽  
Vol 32 (S1) ◽  
pp. S35-S39 ◽  
Author(s):  
Andreas Leineweber
Keyword(s):  
Rietveld Refinement ◽  
Diffraction Data ◽  
High Symmetry ◽  
Line Broadening ◽  
Additional Information ◽  
Isotropic Line ◽  
Symmetry Model ◽  
Symmetry Structure ◽  
The Given ◽  
Low Symmetry

Crystal structure determination on the basis of powder diffraction data frequently involves the question how the given diffraction data with some appreciably hkl-dependent line broadening should be interpreted. In many cases, such line broadening may either: (i) reasonably well be reconciled with a certain high-symmetry structure model or (ii) with a variant of the former with lower symmetry crystal family, which frequently will give a somewhat better fit in Rietveld refinement. In this work, it is shown mathematically that symmetry reduction induced reflection spitting masked by other line broadening contributions, thus leading to some reflection splitting-induced line broadening, shows a similar hkl dependence as typically adopted for anisotropic microstrain broadening with respect to the high-symmetry structure. This implies that Rietveld refinement on the basis of the low-symmetry model (including typically isotropic line broadening) and on the basis of the high-symmetry model with anisotropic microstrain broadening can both lead to similar qualities of the fit. Hence, the refinement results for both possibilities should be carefully considered in combination with possibly available additional information (e.g. results of first-principles calculations) to arrive at adequate conclusions concerning the true symmetry of the material under investigation.

scholarly journals Late Stage Diversification of an Unsymmetrical Ligand Scaffold for Multi-functional cis-Pd2L4 Nanocage Libraries

2020 ◽  
Author(s):  
James Lewis
Keyword(s):  
Self Assembly ◽  
Late Stage ◽  
Combinatorial Libraries ◽  
The Self ◽  
High Symmetry ◽  
Diversification Strategy ◽  
Supramolecular Architectures ◽  
Common Precursor ◽  
Potential Applications ◽  
Low Symmetry

<p>Although many impressive metallo-supramolecular architectures have been reported, they tend towards high symmetry structures and avoid extraneous functionality to ensure high-fidelity in the self-assembly process. This minimalist approach, however, limits the range of accessible structures and thus their potential applications. Herein is described a late stage diversification strategy towards ligand scaffolds that are both low symmetry and incorporate exohedral functional moieties. Key to this design is the use of CuAAC chemistry, as the triazole is capable of acting as both a coordinating heterocycle and a tether between the ligand framework and functional unit simultaneously. In this manner a common precursor was used to generate ligands with various functionalities, allowing control of electronic properties, whilst maintaining the core structure of the resultant <i>cis</i>-Pd<sub>2</sub>L<sub>4</sub> nanocage assemblies. The isostructural nature of the scaffold frameworks enabled formation of combinatorial libraries from the self-assembly of ligand mixtures, generating multi-functional, low-symmetry architectures.</p>

scholarly journals Pseudo Jahn−Teller Origin of the Proton Tunneling in Zundel Cation Containing Water Clusters

2021 ◽  
Vol 57 (11) ◽  
pp. 1149
Author(s):  
I. Geru ◽  
N. Gorinchoy ◽  
I. Balan
Keyword(s):  
Ab Initio ◽  
Electronic Structures ◽  
Water Clusters ◽  
Electronic States ◽  
Adiabatic Potential ◽  
Water Molecules ◽  
High Symmetry ◽  
Proton Tunneling ◽  
Jahn Teller ◽  
Low Symmetry

The pseudo Jahn–Teller (PJT) origin of the proton transfer barrier in the Zundel cation at different O–O distances and in an H5O2+(H2O)4 cluster is revealed by means of  ab initio calculations of their electronic structures and the adiabatic potential energy curves. The vibronic constants in this approach were estimated by fitting the ab initio calculated adiabatic potential to its analytical expression. It is shown also that the high-symmetry nuclear configurations ofproton-centered water clusters of the type H+(H2O)n (n = 6, 4, 3) are unstable with respect to the low-symmetry nuclear distortions leading to forming the dihydronium cation H5O2+ and the appropriate number of water molecules: H2n + 1On+ →  (n – 2)H2O + H5O2+. The reason for this instability and the subsequent decay is the PJT coupling between the ground and excited electronic states.

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