scholarly journals High symmetry or low symmetry, that is the question – high performance Dy(iii) single-ion magnets by electrostatic potential design

2016 ◽  
Vol 7 (1) ◽  
pp. 684-691 ◽  
Author(s):  
Wen-Bin Sun ◽  
Peng-Fei Yan ◽  
Shang-Da Jiang ◽  
Bing-Wu Wang ◽  
Yi-Quan Zhang ◽  
...  
Keyword(s):  
Electrostatic Potential ◽  
High Performance ◽  
High Symmetry ◽  
Suitable Arrangement ◽  
Low Symmetry

A suitable arrangement of the ligand charge can complement a low symmetry system and induce an excellent unexpected SMM behavior.

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?

A boron-exposed TiB3 monolayer with a lower electrostatic-potential surface as a higher-performance anode material for Li-ion and Na-ion batteries

2020 ◽  
Vol 22 (39) ◽  
pp. 22236-22243
Author(s):  
Rong Li ◽  
Yatong Wang ◽  
Li-Chun Xu ◽  
Jiale Shen ◽  
Wenyang Zhao ◽  
...  
Keyword(s):  
Anode Material ◽  
Electrostatic Potential ◽  
Anode Materials ◽  
High Performance ◽  
Potential Surface ◽  
Major Obstacle ◽  
Electrostatic Potential Surface ◽  
Li Ion

The lack of high-performance anode materials has become a major obstacle to the development of Li- and Na-ion batteries.

Comparative study of X-ray charge-density data on CoSb3

2013 ◽  
Vol 69 (6) ◽  
pp. 570-582 ◽  
Author(s):  
Mette Stokkebro Schmøkel ◽  
Lasse Bjerg ◽  
Finn Krebs Larsen ◽  
Jacob Overgaard ◽  
Simone Cenedese ◽  
...  
Keyword(s):  
Charge Density ◽  
High Performance ◽  
Theoretical Data ◽  
High Energy ◽  
Data Sets ◽  
High Symmetry ◽  
X Ray ◽  
Structure Factors ◽  
Small Crystals ◽  
Density Analysis

CoSb3is an example of a highly challenging case for experimental charge-density analysis due to the heavy elements (suitability factor of ∼0.01), the perfect crystallinity and the high symmetry of the compound. It is part of a family of host–guest structures that are potential candidates for use as high-performance thermoelectric materials. Obtaining and analysing accurate charge densities of the undoped host structure potentially can improve the understanding of the thermoelectric properties of this family of materials. In a previous study, analysis of the electron density gave a picture of covalent Co–Sb and Sb–Sb interactions together with relatively low atomic charges based on state-of-the-art experimental and theoretical data. In the current study, several experimental X-ray diffraction data sets collected on the empty CoSb3framework are compared in order to probe the experimental requirements for obtaining data of high enough quality for charge-density analysis even in the case of very unsuitable crystals. Furthermore, the quality of the experimental structure factors is tested by comparison with theoretical structure factors obtained from periodic DFT calculations. The results clearly show that, in the current study, the data collected on high-intensity, high-energy synchrotron sources and very small crystals are superior to data collected at conventional sources, and in fact necessary for a meaningful charge-density study, primarily due to greatly diminished effects of extinction and absorption which are difficult to correct for with sufficient accuracy.

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 Chelate Coordination Compounds as a New Class of High-Energy Materials: The Case of Nitro-Bis(Acetylacetonato) Complexes

Molecules ◽  
2021 ◽  
Vol 26 (18) ◽  
pp. 5438
Author(s):  
Danijela S. Kretić ◽  
Ivana S. Veljković ◽  
Aleksandra B. Đunović ◽  
Dušan Ž. Veljković
Keyword(s):  
Electrostatic Potential ◽  
High Performance ◽  
Density Functional ◽  
High Efficiency ◽  
High Energy ◽  
Molecular Surface ◽  
Energy Materials ◽  
Dissociation Energies ◽  
Central Regions ◽  
And Performance

The existence of areas of strongly positive electrostatic potential in the central regions of the molecular surface of high-energy molecules is a strong indicator that these compounds are very sensitive towards detonation. Development of high-energy compounds with reduced sensitivity towards detonation and high efficiency is hard to achieve since the energetic molecules with high performance are usually very sensitive. Here we used Density Functional Theory (DFT) calculations to study a series of bis(acetylacetonato) and nitro-bis(acetylacetonato) complexes and to elucidate their potential application as energy compounds with moderate sensitivities. We calculated electrostatic potential maps for these molecules and analyzed values of positive potential in the central portions of molecular surfaces in the context of their sensitivity towards detonation. Results of the analysis of the electrostatic potential demonstrated that nitro-bis(acetylacetonato) complexes of Cu and Zn have similar values of electrostatic potential in the central regions (25.25 and 25.06 kcal/mol, respectively) as conventional explosives like TNT (23.76 kcal/mol). Results of analysis of electrostatic potentials and bond dissociation energies for the C-NO2 bond indicate that nitro-bis(acetylacetonato) complexes could be used as potential energetic compounds with satisfactory sensitivity and performance.

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.

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