The unified quantum mechanical structure of tubular molecular rotors with multiple equivalent global minimum structures: the 18*C2h → D9d case of La-[B2@B18]-La

2021 ◽  
Vol 23 (35) ◽  
pp. 19146-19149
Author(s):  
Xiao-Qin Lu ◽  
Yuan Man ◽  
Vincent Ruß ◽  
Yonghong Xu ◽  
Yonggang Yang ◽  
...  
Keyword(s):  
Global Minimum ◽  
Molecular Rotors ◽  
Quantum Mechanical ◽  
High Symmetry ◽  
Quantum Structure ◽  
Mechanical Structure ◽  
Low Symmetry

From 18 equivalent global minimum structures of a tubular rotor with a low symmetry (C2h) to a unified quantum structure with a high symmetry (D9d).

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?

Quantum Mechanical Structure−Activity Relationship Analyses for Skin Sensitization

2005 ◽  
Vol 45 (4) ◽  
pp. 924-929 ◽  
Author(s):  
Matthew D. Miller ◽  
David M. Yourtee ◽  
Alan G. Glaros ◽  
Cecil C. Chappelow ◽  
J. David Eick ◽  
...  
Keyword(s):  
Structure Activity Relationship ◽  
Activity Relationship ◽  
Quantum Mechanical ◽  
Skin Sensitization ◽  
Mechanical Structure ◽  
Structure Activity

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.

First principles investigation of the diffusion of interstitial Cu, Ag and Au in ZnTe

2015 ◽  
Vol 29 (19) ◽  
pp. 1550130
Author(s):  
Li An Chen ◽  
Xing Feng Zhu ◽  
Ling Fu Chen
Keyword(s):  
First Principles ◽  
Global Minimum ◽  
Minimum Energy ◽  
Relative Size ◽  
High Symmetry ◽  
First Principles Calculations ◽  
Energy Diffusion ◽  
Straight Line ◽  
Energy Location ◽  
Diffusion Mechanisms

The diffusion is of great significance in many applications when the impurities are employed to tune the semiconductor's electrical or optical properties. It is necessary to understand how dopant defects diffuse in semiconductors. Using first-principles calculations, we consider interstitial diffusion mechanisms and calculate the migration barrier energies of interstitial Cu, Ag and Au atoms in II–VI compounds ZnTe. We find that the relative size of dopant and bulk atoms is an important factor which affects the diffusion behavior. The high symmetry Tc site, which is tetrahedrally coordinated by four cation atoms, is the global minimum energy location for Ag and Au interstitials. The size of Cu adatom is small, so Cu is more stable when it locates at the Ta site which is tetrahedrally coordinated by four anion atoms. But the global minimum energy location for Cu interstitials is M site which is of smaller space than Ta. Cu adatoms show an asymmetric curve of energy diffusion barrier with two energetically distinct extremum in the pathway. Ag diffuses along nearly straight line paths along [111] or equivalent directions. Diffusion for Cu or Au deviates from the straight line paths along 〈111〉 avoiding high symmetric sites.

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.

THE PHOTOINITIATED ADDITION OF BUTYL MERCAPTAN TO CONJUGATED AND UNCONJUGATED DOUBLE BONDS

1954 ◽  
Vol 32 (12) ◽  
pp. 1078-1091 ◽  
Author(s):  
R. Back ◽  
G. Trick ◽  
C. McDonald ◽  
C. Sivertz
Keyword(s):  
Double Bond ◽  
Transfer Rate ◽  
Kinetic Mechanism ◽  
Quantum Mechanical ◽  
Double Bonds ◽  
General Survey ◽  
Mechanical Structure ◽  
Sector Method

This study elucidates the details of a typical initiation encountered in polymerization. A kinetic mechanism for the photoinitiated addition of normal butyl mercaptan to single and conjugated double bonds is proposed, and the corresponding velocity constants namely the attack kα, the transfer kct, and the termination kt have been measured employing a sector method. For the concentrations employed in this work the over-all rate of addition to the double bond is determined by the transfer rate of the composite mercapto monomer radical, while the capture of initiating radicals depends on the rate of attack of the mercaptyl radicals on the double bonds. The transfer rate is about 1000 times faster for a pentenyl than for a conjugated styryl radical, while the attack step is estimated to be several hundred times faster for the conjugated monomer. These conclusions are shown to be consistent with results observed when conjugated and unconjugated monomers are in competition, and are in agreement with the quantum mechanical structure of the radicals and molecules involved. This work reports a general survey of the field, and subsequent papers will extend the observations.

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