Artykuły w czasopismach: „Structural Inversion Symmetry”

1

D’Iorio, Matthew, i Ken Dewar. "Replication-associated inversions are the dominant form of bacterial chromosome structural variation". Life Science Alliance 6, nr 1 (19.10.2022): e202201434. http://dx.doi.org/10.26508/lsa.202201434.

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The structural arrangements of bacterial chromosomes vary widely between closely related species and can result in significant phenotypic outcomes. The appearance of large-scale chromosomal inversions that are symmetric relative to markers for the origin of replication (OriC) has been previously observed; however, the overall prevalence of replication-associated structural rearrangements (RASRs) in bacteria and their causal mechanisms are currently unknown. Here, we systematically identify the locations of RASRs in species with multiple complete-sequenced genomes and investigate potential mediating biological mechanisms. We found that 247 of 313 species contained sequences with at least one large (>50 Kb) inversion in their sequence comparisons, and the aggregated inversion distances away from symmetry were normally distributed with a mean of zero. Many inversions that were offset from dnaA were found to be centered on a different marker for theOriC. Instances of flanking repeats provide evidence that breaks formed during the replication process could be repaired to opposing positions. We also found a strong relationship between the later stages of replication and the range in distance variation from symmetry.

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Budzianowski, Armand, i Andrzej Katrusiak. "Coupling of the lactone-ring conformation with crystal symmetry in 6-hydroxy-4,4,5,7,8-pentamethyl-3,4-dihydrocoumarin". Acta Crystallographica Section B Structural Science 58, nr 1 (24.01.2001): 125–33. http://dx.doi.org/10.1107/s0108768101017955.

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Conformational disorder and inversions of the lactone ring induce structural transformations in the crystals of 6-hydroxy-4,4,5,7,8-pentamethyl-3,4-dihydrocoumarin, C14H18O3. The onset of ordering of the lactone ring at 300 K proceeds continuously, changes the space group from P21/m to P21/c and doubles the unit cell; the abrupt inversion of the lactone rings at 225 K changes the crystal translational symmetry in the (010) plane. The mechanism combining the molecular conformation and dynamics with the crystal structure, its symmetry, and phase transitions is presented.

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Kobayashi, Aoi, Yoshiki Takano i Satoshi Demura. "Observation of the Specific Heat Jump in the Se-Substituted MoTe2 Single Crystals". Materials 15, nr 11 (25.05.2022): 3782. http://dx.doi.org/10.3390/ma15113782.

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1T’-MoTe2 has gained considerable attention owing to its topological character. This material undergoes spatial inversion symmetry at 300 K. A structural transition to the Td phase, which is represented by a kink in the resistivity, was observed below 250 K without inversion symmetry along the c-axis, while superconductivity was observed at 0.1 K. Substitution of Se into this material suppressed the appearance of the kink structure and increased the superconducting transition temperature to 2 K, which is consistent with previously reported results on polycrystalline samples. However, a specific heat jump was observed in the obtained single crystals, which did not exhibit kink structures in their resistivity. The results suggest that the Td structure was not suppressed entirely after Se substitution and that superconductivity was achieved without inversion symmetry.

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Norell, Jesper, Raphael M. Jay, Markus Hantschmann, Sebastian Eckert, Meiyuan Guo, Kelly J. Gaffney, Philippe Wernet, Marcus Lundberg, Alexander Föhlisch i Michael Odelius. "Fingerprints of electronic, spin and structural dynamics from resonant inelastic soft X-ray scattering in transient photo-chemical species". Physical Chemistry Chemical Physics 20, nr 10 (2018): 7243–53. http://dx.doi.org/10.1039/c7cp08326b.

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Krüger, Ekkehard. "Structural Distortion Stabilizing the Antiferromagnetic and Insulating Ground State of NiO". Symmetry 12, nr 1 (26.12.2019): 56. http://dx.doi.org/10.3390/sym12010056.

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We report evidence that the experimentally observed small deformation of antiferromagnetic NiO modifies the symmetry of the crystal in such a way that the antiferromagnetic state becomes an eigenstate of the electronic Hamiltonian. This deformation closely resembles a rhombohedral contraction, but does not possess the perfect symmetry of a trigonal (rhombohedral) space group. We determine the monoclinic base centered magnetic space group of the antiferromagnetic structure within the deformed crystal which is strongly influenced by the time-inversion symmetry of the Hamiltonian. The antiferromagnetic state is evidently stabilized by a nonadiabatic atomic-like motion of the electrons near the Fermi level. This atomic-like motion is characterized by the symmetry of the Bloch functions near the Fermi level and provides in NiO a perfect basis for a Mott insulator in the antiferromagnetic phase.

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Weng, Ze F., W. D. Sam Motherwell i Jacqueline M. Cole. "Tormat: a program for the automated structural alignment of molecular conformations". Journal of Applied Crystallography 41, nr 5 (16.08.2008): 955–57. http://dx.doi.org/10.1107/s002188980802308x.

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A method is described which enables automated superimposition of molecular conformations by the matching of chemical graphs, allowing for topological symmetry in the molecular structure. This algorithm is implemented in the programTormat. The implemented method makes allowance for enantiomer inversion, explicit and implicit treatment of H atoms, and partial structure alignment.

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Nishimura, T., M. Haruta, D. H. Kim, Y. Shiota, H. Iwaki, D. Kan, T. Moriyama, H. Kurata i T. Ono. "Fabrication of Ferrimagnetic Co/Gd/Pt Multilayers with Structural Inversion Symmetry Breaking". Journal of the Magnetics Society of Japan 44, nr 1 (1.01.2020): 9–14. http://dx.doi.org/10.3379/msjmag.2001r002.

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Krüger, Ekkehard, i Horst P. Strunk. "Structural Distortion in Antiferromagnetic BaFe2As2 as a Result of Time-Inversion Symmetry". Journal of Superconductivity and Novel Magnetism 27, nr 2 (27.08.2013): 601–12. http://dx.doi.org/10.1007/s10948-013-2324-z.

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Marković, Igor, Matthew D. Watson, Oliver J. Clark, Federico Mazzola, Edgar Abarca Morales, Chris A. Hooley, Helge Rosner i in. "Electronically driven spin-reorientation transition of the correlated polar metal Ca3Ru2O7". Proceedings of the National Academy of Sciences 117, nr 27 (23.06.2020): 15524–29. http://dx.doi.org/10.1073/pnas.2003671117.

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The interplay between spin–orbit coupling and structural inversion symmetry breaking in solids has generated much interest due to the nontrivial spin and magnetic textures which can result. Such studies are typically focused on systems where large atomic number elements lead to strong spin–orbit coupling, in turn rendering electronic correlations weak. In contrast, here we investigate the temperature-dependent electronic structure ofCa3Ru2O7, a4doxide metal for which both correlations and spin–orbit coupling are pronounced and in which octahedral tilts and rotations combine to mediate both global and local inversion symmetry-breaking polar distortions. Our angle-resolved photoemission measurements reveal the destruction of a large hole-like Fermi surface upon cooling through a coupled structural and spin-reorientation transition at 48 K, accompanied by a sudden onset of quasiparticle coherence. We demonstrate how these result from band hybridization mediated by a hidden Rashba-type spin–orbit coupling. This is enabled by the bulk structural distortions and unlocked when the spin reorients perpendicular to the local symmetry-breaking potential at the Ru sites. We argue that the electronic energy gain associated with the band hybridization is actually the key driver for the phase transition, reflecting a delicate interplay between spin–orbit coupling and strong electronic correlations and revealing a route to control magnetic ordering in solids.

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Dewangan, Pawan, i Ilya Tsvankin. "Modeling and inversion of PS-wave moveout asymmetry for tilted TI media: Part 2 — Dipping TTI layer". GEOPHYSICS 71, nr 4 (lipiec 2006): D123—D134. http://dx.doi.org/10.1190/1.2210987.

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Dipping transversely isotropic layers with a tilted symmetry axis (TTI media) cause serious imaging problems in fold-and-thrust belts and near salt domes. Here, we apply the modified [Formula: see text] method introduced in Part 1 to the inversion of long-offset PP and PS reflection data for the parameters of a TTI layer with the symmetry axis orthogonal to the bedding. The inversion algorithm combines the time- and offset-asymmetry attributes of the PSV-wave with the hyperbolic PP- and SS-wave moveout in the symmetry-axis plane (i.e., the vertical plane that contains the symmetry axis). The weak-anisotropy approximations for the moveout-asymmetry attributes, verified by numerical analysis, indicate that small-offset (leading) terms do not contain independent information for the inversion. Therefore, the parameter-estimation algorithm relies on PS data recorded at large offsets (the offset-to-depth ratio has to reach at least two), which makes the results generally less stable than those for a horizontal TTI layer in Part1. The least-resolved parameter is Thomsen’s coefficient [Formula: see text]that does not directly influence the moveout of either pure or converted modes. Still, the contribution of the PS-wave asymmetry attributes helps to constrain the TTI model for large tilts [Formula: see text] of the symmetry axis [Formula: see text]. The accuracy of the inversion for large tilts can be improved further by using wide-azimuth PP and PS reflections. With high-quality PS data, the inversion remains feasible for moderate tilts [Formula: see text], but it breaks down for models with smaller values of [Formula: see text] in which the moveout asymmetry is too weak. The tilt itself and several combinations of the medium parameters (e.g., the ratio of the P- and S-wave velocities in the symmetry direction), however, are well constrained for all symmetry-axis orientations. The results of Parts 1 and 2 show that 2D measurements of the PS-wave asymmetry attributes can be used effectively in anisotropic velocity analysis for TTI media. In addition to providing an improved velocity model for imaging beneath TTI beds, our algorithms yield information for lithology discrimination and structural interpretation.

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Marsh, Richard E., i Anthony L. Spek. "Use of software to search for higher symmetry: space group C2". Acta Crystallographica Section B Structural Science 57, nr 6 (29.11.2001): 800–805. http://dx.doi.org/10.1107/s0108768101014331.

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From a search of the October 2000 release of the Cambridge Structural Database we find coordinate data for approximately 1500 entries under space group No. 5: C2 or, occasionally, A2, I2 or B112. Software designed to detect cases of missed higher symmetry identified 144 entries for detailed inspection. Of these, 50 should, we believe, be revised to space groups of higher symmetry. The most common revision is to space group C2/m, which entails adding a center of inversion and usually results in important changes in bond lengths and angles.

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Wiscons, Ren A., i Adam J. Matzger. "Utilizing plane group symmetry to favor noncentrosymmetry in three-dimensional crystals". Canadian Journal of Chemistry 98, nr 7 (lipiec 2020): 327–31. http://dx.doi.org/10.1139/cjc-2019-0402.

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Materials that lack inversion symmetry (noncentrosymmetric) demonstrate a diversity of desirable optical and electronic properties in bulk such as second harmonic generation, chiral emission, and piezo-, pyro-, and ferro-electricity. Unfortunately, it is challenging to reliably access noncentrosymmetric packing motifs because the closest packing of molecules is often achieved through inversion symmetry operators, leading to the relatively low occurrence of noncentrosymmetry in organic crystals. In this study, the occurrence of noncentrosymmetry in materials that adopt planar packing motifs is investigated because molecular species achieve closest packing in two dimensions through rotations and (or) glides, symmetry operators that do not individually lead to centrosymmetry. It is found that of the 18 crystal structures investigated here adopting planar packing motifs, 13 structures (72%) are noncentrosymmetric showing in-plane polarization. The 13 noncentrosymmetric crystal structures differ from the centrosymmetric structures by directional halogen bonding interactions or steric collisions that align the polarization directions of neighboring layers, leading to bulk structural polarity. The results from this investigation will be of use for designing noncentrosymmetric materials for application in optical and electronic devices.

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Banno, Hiroki, Takaaki Hanai, Toru Asaka, Koji Kimoto, Hiromi Nakano i Koichiro Fukuda. "Electron-density distribution and disordered crystal structure of 12H-SiAlON, SiAl5O2N5". Powder Diffraction 29, nr 4 (10.06.2014): 318–24. http://dx.doi.org/10.1017/s0885715614000396.

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The crystal structure of SiAl5O2N5 was characterized by laboratory X-ray powder diffraction (CuKα1). The title compound is hexagonal with space group P63/mmc (Z = 2). The unit-cell dimensions are a = 0.303153(3) nm, c = 3.28153(3) nm, and V = 0.261178(5) nm3. The initial structural model was successfully derived by the direct methods and further refined by the Rietveld method. The final structural model showed the positional disordering of two of the four (Si,Al) sites. The maximum-entropy method-based pattern fitting (MPF) method was used to confirm the validity of the split-atom model, in which conventional structure bias caused by assuming intensity partitioning was minimized. The reliability indices calculated from the MPF were Rwp = 5.00%, S (=Rwp/Re) = 1.25, Rp = 3.76%, RB = 1.26%, and RF = 0.90%. The disordered crystal structure was successfully described by overlapping four types of domains with ordered atom arrangements. The distribution of atomic positions in each of the domains can be achieved in the space group P63mc. Two of the four types of domains are related by a pseudo-symmetry inversion, and the two remaining domains also have each other the inversion pseudo-symmetry.

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Hu, Yang, Fred Florio, Zhizhong Chen, W. Adam Phelan, Maxime A. Siegler, Zhe Zhou, Yuwei Guo i in. "A chiral switchable photovoltaic ferroelectric 1D perovskite". Science Advances 6, nr 9 (luty 2020): eaay4213. http://dx.doi.org/10.1126/sciadv.aay4213.

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Spin and valley degrees of freedom in materials without inversion symmetry promise previously unknown device functionalities, such as spin-valleytronics. Control of material symmetry with electric fields (ferroelectricity), while breaking additional symmetries, including mirror symmetry, could yield phenomena where chirality, spin, valley, and crystal potential are strongly coupled. Here we report the synthesis of a halide perovskite semiconductor that is simultaneously photoferroelectricity switchable and chiral. Spectroscopic and structural analysis, and first-principles calculations, determine the material to be a previously unknown low-dimensional hybrid perovskite (R)-(−)-1-cyclohexylethylammonium/(S)-(+)-1 cyclohexylethylammonium) PbI3. Optical and electrical measurements characterize its semiconducting, ferroelectric, switchable pyroelectricity and switchable photoferroelectric properties. Temperature dependent structural, dielectric and transport measurements reveal a ferroelectric-paraelectric phase transition. Circular dichroism spectroscopy confirms its chirality. The development of a material with such a combination of these properties will facilitate the exploration of phenomena such as electric field and chiral enantiomer–dependent Rashba-Dresselhaus splitting and circular photogalvanic effects.

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Niesner, Daniel, Martin Hauck, Shreetu Shrestha, Ievgen Levchuk, Gebhard J. Matt, Andres Osvet, Miroslaw Batentschuk, Christoph Brabec, Heiko B. Weber i Thomas Fauster. "Structural fluctuations cause spin-split states in tetragonal (CH3NH3)PbI3 as evidenced by the circular photogalvanic effect". Proceedings of the National Academy of Sciences 115, nr 38 (4.09.2018): 9509–14. http://dx.doi.org/10.1073/pnas.1805422115.

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Lead halide perovskites are used in thin-film solar cells, which owe their high efficiency to the long lifetimes of photocarriers. Various calculations find that a dynamical Rashba effect could significantly contribute to these long lifetimes. This effect is predicted to cause a spin splitting of the electronic bands of inversion-symmetric crystalline materials at finite temperatures, resulting in a slightly indirect band gap. Direct experimental evidence of the existence or the strength of the spin splitting is lacking. Here, we resonantly excite photocurrents in single crystalline (CH3NH3)PbI3 with circularly polarized light to clarify the existence of spin splittings in the band structure. We observe a circular photogalvanic effect, i.e., the photocurrent depends on the light helicity, in both orthorhombic and tetragonal (CH3NH3)PbI3. At room temperature, the effect peaks for excitation photon energies ΔE=110 meV below the direct optical band gap. Temperature-dependent measurements reveal a sign change of the effect at the orthorhombic–tetragonal phase transition, indicating different microscopic origins in the two phases. Within the tetragonal phase, both ΔE and the amplitude of the circular photogalvanic effect increase with temperature. Our findings support a dynamical Rashba effect in this phase, i.e., a spin splitting caused by thermally induced structural fluctuations which break inversion symmetry.

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Liu, Wen-Rong, Liang Zhang, Xiao-Jing Dong, Wei-Xiao Ji, Pei-Ji Wang i Chang-Wen Zhang. "Spin–orbit stable dirac nodal line in monolayer B₆O". Chinese Physics B 31, nr 3 (1.03.2022): 037305. http://dx.doi.org/10.1088/1674-1056/ac4cba.

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The two-dimensional (2D) materials with nodal line band crossing have been attracting great research interest. However, it remains a challenge to find high-stable nodal line structure in 2D systems. Herein, based on the first-principles calculations and theoretical analysis, we propose that monolayer B6O possesses symmetry protected Dirac nodal line (DNL) state, with its Fermi velocity of 106 m/s in the same order of magnitude as that of graphene. The origin of DNL fermions is induced by coexistence of time-reversal symmetry and inversion symmetry. A two-band tight-binding model is further given to understand the mechanism of DNL. Considering its robustness against spin–orbit coupling (SOC) and high structural stability, these results suggest monolayer B6O as a new platform for realizing future high-speed low-dissipation devices.

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Johnson, Roger, Laurent Chapon, Kun Cao, Pascal Manuel, Alessandro Bombardi, Sunil Nair, Sang-Wook Cheong i Paolo Radaelli. "The roles of chirality and polarity in novel multiferroics: MnSb2O6and Cu3Nb2O8". Acta Crystallographica Section A Foundations and Advances 70, a1 (5.08.2014): C386. http://dx.doi.org/10.1107/s2053273314096132.

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At room temperature Cu3Nb2O8 has a centrosymmetric, triclinic crystal structure. If cooled below 24 K, the copper magnetic moments order with a complex, generalized helicoidal magnetic structure that breaks inversion symmetry, giving rise to ferroelectricity. Unusually, the direction of the induced electric polarization vector with respect to the helicoidal spin rotation cannot be reconciled by conventional theories of magneto-electric coupling. Instead, we show that the observed multiferroic properties of Cu3Nb2O8 may be explained through a phenomenological analysis based upon coupling between the magnetic chirality, electric polarity, and a structural axial rotation. Trigonal MnSb2O6 crystallizes with a chiral crystal structure. Typically, magnetic materials with a chiral crystal lattice order with a chiral magnetic structure, where the magnetic exchange interactions and anisotropies follow the symmetry of the lattice. The magnetism of MnSi is a classic example of this scenario, in which exotic skyrmion phases emerge out of a helical magnetic state. To the contrary, we show that the low temperature magnetic structure of MnSb2O6 is cycloidal, described by a magnetic polarity as opposed to a chirality. We demonstrate through ab-initio calculations that this magnetic structure is in fact the ground state of the symmetric-exchange Heisenberg spin Hamiltonian, which has higher symmetry than the underlying crystal lattice. Furthermore, the phenomenology may be understood by considering the coupling between structural chirality, magnetic polarity, and a magnetic axial rotation. As a result, we predict MnSb2O6 to be multiferroic with a weak ferroelectric polarization.

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Figueiras, Fábio G. N., Igor K. Bdikin, Vitor B. S. Amaral i Andrei L. Kholkin. "Local bias induced ferroelectricity in manganites with competing charge and orbital order states". Phys. Chem. Chem. Phys. 16, nr 10 (2014): 4977–81. http://dx.doi.org/10.1039/c4cp00075g.

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Perovskite-type manganites, such as Pr_1−xCa_xMnO₃, La_1−xCa_xMnO₃ and La_1−xSr_xMnO₃ solid solutions, are set forth as a case study of ferroelectricity formation mechanisms associated with the appearance of site- and bond-centered orbital ordering which breaks structural inversion symmetry.

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Pelzer, Kenley, Nicholas Schwarz i Ross Harder. "Removal of spurious data in Bragg coherent diffraction imaging: an algorithm for automated data preprocessing". Journal of Applied Crystallography 54, nr 2 (18.03.2021): 523–32. http://dx.doi.org/10.1107/s1600576721000819.

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Bragg coherent diffraction imaging (BCDI) provides a powerful tool for obtaining high-resolution structural information from nanocrystalline materials. Here a BCDI sample consisting of a large number of randomly oriented nanoscale crystals is considered. Ideally, only one crystal is oriented to produce a Bragg peak on the detector. However, diffraction from other crystals often produces additional signals on the detector. Before the measured diffraction patterns can be processed into structural images, scientists routinely need to manually identify and remove the `alien' intensities from sources other than the intended crystal. With the development of modern high-coherence storage rings, such as the upgraded Advanced Photon Source (APS), the already slow process of manual preprocessing will be untenable for the large volumes of data that will be produced. An automated method of identifying and deleting alien intensities is proposed. This method exploits the fact that BCDI of a perfect crystal produces diffraction data with inversion symmetry around the Bragg peak. This approach uses the machine learning clustering method DBSCAN to distinguish between diffraction from multiple sources, and then calculates cluster size and inversion symmetry to assess whether clusters of intensity belong to desired data or alien signals. This approach can dramatically reduce the amount of time spent manually processing data, allowing BCDI data processing capabilities to keep pace with the technological advances of fourth-generation synchrotron light sources.

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Wheeler, Kraig, Katriel Sahlstrom, Russell Wells, Franklin Ekelem, Almat Yeraly i Diana Schepens. "Departures from near inversion symmetry using amino acid hydrogen oxalate quasiracemates". Acta Crystallographica Section A Foundations and Advances 78, a1 (29.07.2022): a113. http://dx.doi.org/10.1107/s2053273322098862.

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Gnewuch, Stephanie, i Efrain Rodriguez. "Centers of spatial and time inversion symmetry in magnetoelectric crystalline materials". Acta Crystallographica Section A Foundations and Advances 77, a1 (30.07.2021): a191. http://dx.doi.org/10.1107/s0108767321098081.

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Miras, Adolfo, Agustín Cota i Domingo Martín. "GESUS, an Interactive Computer Application for Teaching and Learning the Space Groups of Symmetry". Education Sciences 12, nr 2 (26.01.2022): 85. http://dx.doi.org/10.3390/educsci12020085.

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This paper describes a digital application designed for learning Space Groups of Symmetry (SGS). It teaches how to recognize the operations performed by the symmetry elements, both point (or 2D) operators (proper and improper rotations, including mirroring, inversion, and other rotoinversions), and space (or 3D) operators (screw axes and glide planes), as well as their combinations with the translations of the lattice. The software applies a 3D space vision to identify the elements of symmetry compatible with the proposed structural models. The symbols of internationally accepted representation are used. The system, class, and space group of the crystal that agree with the proposed model are solved. Two settings are taken into account in the Monoclinic system. The application self-evaluates and assesses the knowledge acquired, allowing each exercise to be re-done until it is correctly completed with the appropriate recommendations. This application constitutes a useful and easy-to-use tool for SGS learning. It is aimed at beginner students of crystallography, with elementary knowledge about elements of symmetry, Bravais lattices, crystal classes, and wallpaper groups.

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Narayana, Badiadka, Balladka K. Sarojini, Hemmige S. Yathirajan, Ravindranath Rathore i Christopher Glidewell. "Crystal structure of (RS)-(4-chlorophenyl)(pyridin-2-yl)methanol". Acta Crystallographica Section E Crystallographic Communications 72, nr 1 (1.01.2016): 69–72. http://dx.doi.org/10.1107/s2056989015023154.

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In the title racemic compound, C12H10ClNO, the dihedral angle between the benzene and pyridine rings is 74.34 (6)°. In the crystal, the molecules are linked by O—H...N hydrogen bonds, forming zigzagC(5) [001] chains in which alternatingR- andS-configuration molecules are related byc-glide symmetry. In addition, inversion-related pairs of molecules are linked into dimers by pairs of weak C—Cl...π(pyridyl) interactions, which link the hydrogen-bonded chains into (100) sheets. Structural comparisons are drawn with a number of related compounds.

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Grechka, Vladimir, Andres Pech, Ilya Tsvankin i Baoniu Han. "Velocity analysis for tilted transversely isotropic media: A physical modeling example". GEOPHYSICS 66, nr 3 (maj 2001): 904–10. http://dx.doi.org/10.1190/1.1444980.

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Transverse isotropy with a tilted symmetry axis (TTI media) has been recognized as a common feature of shale formations in overthrust areas, such as the Canadian Foothills. Since TTI layers cause serious problems in conventional imaging, it is important to be able to reconstruct the velocity model suitable for anisotropic depth migration. Here, we discuss the results of anisotropic parameter estimation on a physical‐modeling data set. The model represents a simplified version of a typical overthrust section from the Alberta Foothills, with a horizontal reflector overlaid by a bending transversely isotropic layer. Assuming that the TTI layer is homogeneous and the symmetry axis stays perpendicular to its boundaries, we invert P-wave normal‐moveout (NMO) velocities and zero‐offset traveltimes for the symmetry‐direction velocity V0 and the anisotropic parameters ε and δ. The coefficient ε is obtained using the traveltimes of a wave that crosses a dipping TTI block and reflects from the bottom of the model. The inversion for ε is based on analytic expressions for NMO velocity in media with intermediate dipping interfaces. Our estimates of both anisotropic coefficients are close to their actual values. The errors in the inversion, which are associated primarily with the uncertainties in picking the NMO velocities and traveltimes, can be reduced by a straighforward modification of the acquisition geometry. It should be emphasized that the moveout inversion also gives an accurate estimate of the thickness of the TTI layer, thus reconstructing the correct depth scale of the section. Although the physical model used here was relatively simple, our results demonstrate the principal feasibility of anisotropic velocity analysis and imaging in overthrust areas. The main problems in anisotropic processing for TTI models are likely to be caused by the lateral variation of the velocity field and overall structural complexity.

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Fábián, László, i Carolyn Pratt Brock. "A list of organic kryptoracemates". Acta Crystallographica Section B Structural Science 66, nr 1 (22.01.2010): 94–103. http://dx.doi.org/10.1107/s0108768109053610.

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A list of 181 organic kryptoracemates has been compiled. This class of crystallographic oddities is made up of racemic compounds (i.e. pairs of resolvable enantiomers) that happen to crystallize in Sohnke space groups (i.e. groups that include only proper symmetry operations). Most (151) of the 181 structures could have crystallized as ordered structures in non-Sohnke groups. The remaining 30 structures do not fully meet this criterion but would have been classified as kryptoracemates by previous authors. Examples were found and checked with the aid of available software for searching the Cambridge Structural Database, for generating and comparing InChI strings, and for validating crystal structures. The pairs of enantiomers in the true kryptoracemates usually have very similar conformations; often the match is near-perfect. There is a pseudosymmetric relationship of the enantiomers in about 60% of the kryptoracemate structures, but the deviations from inversion or glide symmetry are usually quite easy to spot. Kryptoracemates were found to account for 0.1% of all organic structures containing either a racemic compound, a meso molecule, or some other achiral molecule. The centroid of a pair of enantiomers is more likely (99.9% versus 99% probability) to be located on an inversion center than is the centroid of a potentially centrosymmetric molecule.

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Asaka, Toru, Tatsunari Kudo, Hiroki Banno, Shiro Funahashi, Naoto Hirosaki i Koichiro Fukuda. "Electron density distribution and crystal structure of 21R-AlON, Al7O3N5". Powder Diffraction 28, nr 3 (31.05.2013): 171–77. http://dx.doi.org/10.1017/s0885715613000419.

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The crystal structure of Al7O3N5 was characterized by laboratory X-ray powder diffraction (CuKα1). The title compound is trigonal with a space group R3m (centrosymmetric). The hexagonal unit-cell dimensions (Z = 3) are a = 0.305 06(1) nm, c = 5.7216(1) nm, and V = 0.461 11(2) nm3. The initial structural model was derived by the charge-flipping method and refined by the Rietveld method. The final structural model showed the positional disordering of two of the four Al sites. The maximum-entropy method-based pattern fitting method was used to confirm the validity of the split-atom model, in which conventional structure bias caused by assuming intensity partitioning was minimized. The disordered crystal structure was successfully described by overlapping five types of domains with ordered atom arrangements. The distribution of atomic positions in one of the five types of domains can be achieved in the space group R3m. The atom arrangements in the four other domains are non-centrosymmetric with the space group R3m. Two of the four types of domains are related by a pseudo-symmetrical inversion, and the two remaining domains also have each other in the inversion pseudo-symmetry.

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Abrahams, S. C. "Systematic prediction of new ferroelectrics in space group R3. II". Acta Crystallographica Section B Structural Science 63, nr 2 (16.03.2007): 257–69. http://dx.doi.org/10.1107/s0108768107005290.

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Release 2006/1 of the Inorganic Crystal Structure Database contains 155 entries under space group R3. Atomic coordinate analysis of the first 81 structures, with 52 different structure types, in Part I [Abrahams (2006). Acta Cryst. B62, 26–41] identified a total of 18 new types that satisfy the structural criteria for ferroelectricity, five that are more likely to have or undergo a transition to 3m symmetry, 19 more likely to be or undergo a transition to nonpolar symmetry and ten with a lower property predictability. Coordinate analysis of the remaining 71 entries with 54 different structure types in Part II leads to 11 materials including Al4B6O15, PbTa3(PO4)(P2O7)3.5, the KCd4Ga5S12 family, the LiZnPO4 family, Ca3Nb1.95O8V0.05 and Mn4Ta2O9 as new candidates which satisfy the structural criteria, together with the three known ferroelectrics Na3MoO3F3, Pb2ScTaO6, and RbTi2(PO4)3 at 6.2 GPa. Two additional ferroelectric predictions are at a lower level of confidence. The analysis also reveals nine materials, two of which are isostructural, that more likely belong or are capable of undergoing a transition to crystal class 3m. There are 14 additional structure types which are more likely to be nonpolar or undergo a transition to nonpolarity, ten have reduced predictive properties, with a further nine for which the space group is expected to remain R3 over the full thermal stability range. The increasing use of methods for identifying overlooked inversion centers in structural determinations may be extended by using coordinate analysis for detecting additional commonly overlooked symmetry elements.

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Wachter, Erin, Edith C. Glazer, Sean Parkin i Carolyn Pratt Brock. "An exceptional 5:4 enantiomeric structure". Acta Crystallographica Section B Structural Science, Crystal Engineering and Materials 72, nr 2 (1.04.2016): 223–31. http://dx.doi.org/10.1107/s205252061600127x.

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The only crystals that could be grown from racemic solutions of the PF6−salt of the resolvable cation [Ru(2,9-dimethyl-1,10-phenanthroline)2(dipyrido[3,2-d:2′,3′-f]quinoxaline)]2+have translational symmetry only (space groupP1), contain nine independent sets of ions, and include numerous independent solvent molecules (11 acetone, one diethyl ether and possibly several water molecules). Layers of hydrophobic cations alternate with layers containing most of the anions and solvent molecules. All nine cations have the same basic conformation, which is distorted by the presence of the methyl substituents on the two 1,10-phenanthroline ligands. Four pairs of enantiomeric cations within a layer are related by approximate inversion centers; the ninth cation, which shows no sign of disorder, makes the layer chiral. Within the cation layers stripes parallel to [110] of six cations alternate with stripes of three; the local symmetry and the cation orientations are different in the two stripes. These stripes are reflected in the organization of the anion/solvent layer. Theca80:20 inversion twinning found indicates that enantiomeric preference is transmitted less perfectly across the anion/solvent layer than within the cation layer. The structure is exceptional in having nine independent formula units and an unbalanced set (ratio 4:5) of resolvable enantiomers. The difficulty in growing crystals of this material is consistent with its structural complexity.

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Garcia-Muñoz, Jose Luis, Javier Blasco, Xiaodong Zhang, Arnau Romaguera i Oscar Fabelo. "Magnetic inversion symmetry breaking and spin reorientation in Tb2MnNiO6: a polar strong ferromagnet". Acta Crystallographica Section A Foundations and Advances 75, a2 (18.08.2019): e391-e391. http://dx.doi.org/10.1107/s2053273319091654.

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Schlesinger, Carina, Sonja M. Hammer, Tatiana E. Gorelik i Martin U. Schmidt. "Orientational disorder of monomethyl-quinacridone investigated by Rietveld refinement, structure refinement to the pair distribution function and lattice-energy minimizations". Acta Crystallographica Section B Structural Science, Crystal Engineering and Materials 76, nr 3 (8.05.2020): 353–65. http://dx.doi.org/10.1107/s2052520620003984.

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The crystal structure of the organic pigment 2-monomethyl-quinacridone (Pigment Red 192, C21H14N2O2) was solved from X-ray powder diffraction data. The resulting average structure is described in space group P\overline 1, Z = 1 with the molecule on the inversion centre. The molecules are arranged in chains. The molecules, which have no inversion symmetry, show orientational head-to-tail disorder. In the average structure, the methyl group is disordered and found on both ends of the molecule with an occupancy of 0.5 each. The disorder and the local structure were investigated using various ordered structural models. All models were analysed by three approaches: Rietveld refinement, structure refinement to the pair distribution function (PDF) and lattice-energy minimization. All refinements converged well. The Rietveld refinement provided the average structure and gave no indication of a long-range ordering. The refinement to the PDF turned out to be very sensitive to small structural details, giving insight into the local structure. The lattice-energy minimizations revealed a significantly preferred local ordering of neighbouring molecules along the [0\bar 11] direction. In conclusion, all methods indicate a statistical orientational disorder with a preferred parallel orientation of molecules in one direction. Additionally, electron diffraction revealed twinning and faint diffuse scattering.

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Jaiswal, A. K., R. Schneider, M. Le Tacon i D. Fuchs. "Magnetotransport of SrIrO₃-based heterostructures". AIP Advances 12, nr 3 (1.03.2022): 035120. http://dx.doi.org/10.1063/9.0000325.

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Transition-metal oxide (TMO) based heterostructures provide fertile playground to explore or functionalize novel quantum materials. In this regard, the combination of 3 d and 5 d TMOs have gained special interest because of the simultaneous appearance of strong spin–orbit coupling and electron correlation at the interface of those heterostructures. Artificial breaking of the inversion symmetry in heterostructures may also result in a distinct interfacial Dzyaloshinskii-Moriya interaction (DMI) and the formation of non-collinear magnetic spin structures in case of magnetic TMOs. Among the 5 d TMOs, SrIrO3 (SIO) has gained significant attention because of its large spin–orbit coupling and the semi-metallic ground state, which are highly susceptible to structural distortions. Here, we report on the preparation and the characterisation of structural, electronic and magnetic properties of epitaxial heterostructures consisting of the 5 d TMO SIO and the 3 d antiferromagnetic insulator LaFeO3.

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Nielsen, Kim T., Pernille Harris, Klaus Bechgaard i Frederik C. Krebs. "Structural study of four complexes of the M-N2S2 type derived from diethylphenylazothioformamide and the metals palladium, platinum, copper and nickel". Acta Crystallographica Section B Structural Science 63, nr 1 (15.01.2007): 151–56. http://dx.doi.org/10.1107/s0108768106047306.

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The four electron-transfer complexes trans-(di(N,N-diethyl-(2-phenyldiazenyl)thioformamide-κS,κN 2))nickel, trans-(di(N,N-diethyl-(2-phenyldiazenyl)thioformamide-κS,κN 2))copper, trans-(di(N,N-diethyl-(2-phenyldiazenyl)thioformamide-κS,κN 2))palladium and trans-(di(N,N-diethyl-(2-phenyldiazenyl)thioformamide-κS,κN 2))platinum have been crystallized, and their structures have been determined at low temperature. All the complexes are of the M-N2S2 type. The crystals of both the nickel and the copper complex belong to the tetragonal P41212 system, in which the central metal ion lies on a twofold axis. The tetrahedral molecular symmetry around the central metal ion is unusual for the M-N2S2 electron-transfer complexes. The crystals of the palladium and platinum complexes on the other hand belong to the monoclinic C2/c system in which the metal ion lies on an inversion centre. The molecular symmetry around these metal ions is square planar. It is demonstrated that the π electron density in the ligand planes has a high degree of delocalization. Furthermore, unusually large line broadening of the 1H NMR spectra was observed and investigated as a function of temperature for the palladium complex.

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von Ketelhodt, Julius K., Musa S. D. Manzi, Raymond J. Durrheim i Thomas Fechner. "Seismic vertical transversely isotropic parameter inversion from P- and S-wave cross-borehole measurements in an aquifer environment". GEOPHYSICS 84, nr 3 (1.05.2019): D101—D116. http://dx.doi.org/10.1190/geo2018-0335.1.

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Joint P- and S-wave measurements for tomographic cross-borehole analysis can offer more reliable interpretational insight concerning lithologic and geotechnical parameter variations compared with P-wave measurements on their own. However, anisotropy can have a large influence on S-wave measurements, with the S-wave splitting into two modes. We have developed an inversion for parameters of transversely isotropic with a vertical symmetry axis (VTI) media. Our inversion is based on the traveltime perturbation equation, using cross-gradient constraints to ensure structural similarity for the resulting VTI parameters. We first determine the inversion on a synthetic data set consisting of P-waves and vertically and horizontally polarized S-waves. Subsequently, we evaluate inversion results for a data set comprising jointly measured P-waves and vertically and horizontally polarized S-waves that were acquired in a near-surface ([Formula: see text]) aquifer environment (the Safira research site, Germany). The inverted models indicate that the anisotropy parameters [Formula: see text] and [Formula: see text] are close to zero, with no P-wave anisotropy present. A high [Formula: see text] ratio of up to nine causes considerable SV-wave anisotropy despite the low magnitudes for [Formula: see text] and [Formula: see text]. The SH-wave anisotropy parameter [Formula: see text] is estimated to be between 0.05 and 0.15 in the clay and lignite seams. The S-wave splitting is confirmed by polarization analysis prior to the inversion. The results suggest that S-wave anisotropy may be more severe than P-wave anisotropy in near-surface environments and should be taken into account when interpreting cross-borehole S-wave data.

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Edis, Zehra, i Samir Haj Bloukh. "Darstellung und strukturelle und spektroskopische Charakterisierung der Triiodide [M(12-Krone-4)2]I3 mit M = Na und Rb / Preparation and Structural and Spectroscopic Characterization of Triiodides [M(12-Crown-4)2]I3 with M= Na and Rb". Zeitschrift für Naturforschung B 69, nr 9-10 (1.10.2014): 995–1002. http://dx.doi.org/10.5560/znb.2014-4044.

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Abstract Reddish-brown crystals of [Na(12-crown-4)2]I3 (1) and [Rb(12-crown-4)2]I3 (2) were formed through the reaction of NaI or RbI, I2 and 12-crown-4 in ethanol. Both structures are triclinic, space group P1 with Z = 2. The lattice parameters are a = 8:505(2), b = 14:280(3), c = 10:695(2) Å and α = 89:86(2)°, β = 80:00(2)° and γ = 85:90(2)°; and a = 10:694(2), b = 11:598(2), c = 12:718(2) Å and α = 71:00(2)°, β = 86:97(2)° and γ = 67:710(10)° for 1 and 2, respectively. Both crystal structures contain one independent complex cation without crystallographic symmetry. The anionic parts of both structures consist of two crystallographically independent, isolated, triiodide anions I3- with crystallographic inversion symmetry. The cations are distorted sandwich-like complexes with two 12-crown-4 molecules surrounding the alkali metal atom in the center.

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Dalhus, Bjørn, i Carl Henrik Görbitz. "Non-centrosymmetric racemates: space-group frequencies and conformational similarities between crystallographically independent molecules". Acta Crystallographica Section B Structural Science 56, nr 4 (1.08.2000): 715–19. http://dx.doi.org/10.1107/s0108768100002172.

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DL-Allylglycine (DL-2-amino-4-pentenoic acid, C5H9NO2) yields crystals with Pca21 symmetry and two crystallographically independent yet pseudo-inversion-related enantiomers. The distribution among the common space groups of other crystalline racemates with more than one molecule in the asymmetric unit has been established. The conformational similarities between crystallographically independent enantiomers in 114 non-centrosymmetric racemates were quantified using the r.m.s. deviation for a molecular superposition. The analysis shows that in the majority of crystals the conformations of the crystallographically independent molecules are very similar with mean r.m.s. deviation = 0.190 Å. In almost 80% of the structures the mean r.m.s. deviations is in the interval 0–0.2 Å. It is estimated that racemates constitute 23% of the centrosymmetric organic structures in the Cambridge Structural Database.

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Silvino, Alexandre C., i Juliana M. Torres. "Crystal structure of 1,2-bis[(2-tert-butylphenyl)imino]ethane". Acta Crystallographica Section E Crystallographic Communications 71, nr 6 (9.05.2015): o385—o386. http://dx.doi.org/10.1107/s2056989015008610.

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The whole molecule of the title compound, C22H28N2, (I), is generated by inversion symmetry. The molecule is rather similar to that of 2,3-bis[(2-tert-butylphenyl)imino]butane, (II), a diimine ligand comprising similar structural features [Ferreiraet al.(2006).Acta Cryst.E62, o4282–o4284]. Both ligands crystallize with the –N=C(R)—C(R)=N– group around an inversion centre, in atransconfiguration. Comparing the two structures, it may be noted that the independent planar groups in both molecules [the central link, –N=C(R)—C(R)=N–, and the terminal aromatic ring] subtend an angle of 69.6 (1)° in (II) and 49.4 (2)° in (I). Ferreira and co-workers proposed that such angle deviation may be ascribed to the presence of two non-classical intramolecular hydrogen bonds and steric factors. In fact, in (I), similar non-classical hydrogen bonds are observed, and the larger angular deviation in (II) may be assigned to the presence of methyl groups in the diimino fragment, which can cause steric hindrance due to the presence of bulkytert-butyl substituents in the aromatic rings. The C=N bond lengths are similar in both compounds and agree with comonly accepted values.

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Kelley, Steven P., László Fábián i Carolyn Pratt Brock. "Failures of fractional crystallization: ordered co-crystals of isomers and near isomers". Acta Crystallographica Section B Structural Science 67, nr 1 (15.01.2011): 79–93. http://dx.doi.org/10.1107/s0108768110048135.

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A list of 270 structures of ordered co-crystals of isomers, near isomers and molecules that are almost the same has been compiled. Searches for structures containing isomers could be automated by the use of IUPAC International Chemical Identifier (InChI™) strings but searches for co-crystals of very similar molecules were more labor intensive. Compounds in which the heteromolecular A...B interactions are clearly better than the average of the homomolecular A...A and B...B interactions were excluded. The two largest structural classes found include co-crystals of configurational diastereomers and of quasienantiomers (or quasiracemates). These two groups overlap. There are 114 co-crystals of diastereomers and the same number of quasiracemates, with 71 structures being counted in both groups; together the groups account for 157 structures or 58% of the total. The large number of quasiracemates is strong evidence for inversion symmetry being very favorable for crystal packing. Co-crystallization of two diastereomers is especially likely if a 1,1 switch of a methyl group and an H atom, or of an inversion of a [2.2.1] or [2.2.2] cage, in one of the diastereomers would make the two molecules enantiomers.

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Bouzidi, Chahira, Wafa Frigui i Mohamed Faouzi Zid. "Synthèse et structure cristalline d'un matériau noir AgMnII3(MnIII0,26Al0,74)(MoO4)5". Acta Crystallographica Section E Crystallographic Communications 71, nr 3 (21.02.2015): 299–304. http://dx.doi.org/10.1107/s2056989015003345.

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A new silver aluminium trimanganese pentamolybdate {silver(I) trimanganese(II) aluminium pentakis[tetraoxidomolybdate(VI)]}, AgMnII3(MnIII0,26Al0,74)(MoO4)5, has been synthesized using solid-state methods. The structure is composed ofM2O10dimers,M3O14(M= Mn, Al) trimers and MoO4tetrahedra sharing corners and forming three types of layersA,BandB′. The sequence of the constituting layers isA–BB′–A–BB′, withB′ obtained fromBby inversion symmetry, forming a three-dimensional structure with large channels in which the positionally disordered and partially occupied Ag+ions reside. The MnIIIand AlIIIatoms share the same site,M. AgMnII3(MnIII0,26Al0,74)(MoO4)5is isotypic with the NaMg3X(MoO4)5(X= Al, In) family and with NaFe4(MoO4)5. A comparative structural description is provided between the structure of the title compound and those of related phases containing dimers, trimers and tetramers.

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Millane, Rick P. "The phase problem for one-dimensional crystals". Acta Crystallographica Section A Foundations and Advances 73, nr 2 (16.02.2017): 140–50. http://dx.doi.org/10.1107/s2053273316020386.

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The phase problem for diffraction amplitudes measured from a one-dimensional crystal is examined. In the absence of anya prioriinformation, the solution to this problem is shown to be unique up to a parameterized, low-dimensional set of solutions. Minimal additionala prioriinformation is expected to render the solution unique. The effects of additional information such as positivity, molecular envelope and helical symmetry on uniqueness are characterized. The results are pertinent to structural studies of polymeric and rod-like biomolecular assemblies that form one-dimensional, rather than three-dimensional, crystals. This shows the potential forab initiophasing of diffraction data from single such assemblies measured using new X-ray free-electron laser sources. Such an approach would circumvent the complicated inversion of cylindrically averaged diffraction that is necessary in traditional X-ray fibre diffraction analysis.

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Sikorska, Małgorzata, i Jarosław Chojnacki. "Bis(ammonium) Zoledronate Dihydrate". Journal of Crystallography 2013 (3.10.2013): 1–5. http://dx.doi.org/10.1155/2013/741483.

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Neutralization of 2-(1-imidazole)-1-hydroxyl-1,1′-ethylidenediphosphonic acid (zoledronic acid) by an excess of ammonia yielded bis(ammonium) zoledronate dihydrate, {, 2(H4N+), 2(H2O)}. The product is readily soluble in water and forms monocrystals for which the X-ray structural analysis was carried out. The zoledronic anion is of double negative charge due to deprotonation of three P–OH groups and protonation of the nitrogen in the imidazole ring. The structure is stabilized by extensive network of N–H⋯O and O–H⋯O hydrogen bonds expanding through the crystal in plane (002). The imidazole ring is involved in - stacking interactions with its symmetry equivalents related by inversion centers at (1 0 0) and (1 1/2 0), with distances between centroids (Cg–Cg) of 3.819 (2) and 3.881 (2) Å, respectively.

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Gessmann, Renate, Hans Brückner i Kyriacos Petratos. "Removing the C-terminal protecting group enlarges the crystal size: Z–(Gly–Aib)2–OH·H2O". Acta Crystallographica Section C Structural Chemistry 76, nr 12 (9.11.2020): 1057–61. http://dx.doi.org/10.1107/s2053229620014254.

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The achiral tetrapeptide monohydrate N-(benzyloxycarbonyl)glycyl-α-aminoisobutyrylglycyl-α-aminoisobutyric acid monohydrate, Z–Gly–Aib–Gly–Aib–OH·H2O (Z is benzyloxycarbonyl, Aib is α-aminoisobutyric acid and Gly is glycine) or C20H28N4O7·H2O, exhibits two conformations related by the symmetry operation of an inversion centre. It adopts only one of two possible intramolecular hydrogen bonds in a type I (and I′) β-turn and forms a maximum of intermolecular hydrogen bonds partly mediated by water. The space group, the molecular structure and the crystal packing differ from two already described (Gly–Aib)2 peptides which vary only in the protecting groups. This structure confirms the high structural flexibility of Gly–Aib peptides and points to a strong relationship between intermolecular hydrogen bonding and crystal quality and size.

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Yang, Yongqi, Guangming Cheng, Joanna Blawat, Duncan H. Moseley, Haozhe Wang, Kasey P. Devlin, Yu Yu i in. "Crystal structure and magnetic properties in semiconducting Eu_3−δZn_xSn_yAs₃ with Eu-Eu dimers". Journal of Applied Physics 132, nr 4 (28.07.2022): 043902. http://dx.doi.org/10.1063/5.0094013.

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Magnetic structure and crystal symmetry, which primarily determine the time-reversal and inversion symmetry, may give rise to numerous exotic quantum phenomena in magnetic semiconductors and semimetals when arranged in different patterns. In this work, a new layered magnetic semiconductor, Eu3−δZn xSn yAs3, was discovered and high-quality single crystals were grown using the Sn flux. According to structural characterization by x-ray diffraction and atomic-resolution scanning transmission electron microscopy, Eu3−δZn xSn yAs3 is found to crystallize in a hexagonal symmetry with the space group P63/ mmc (No. 194). After examining different specimens, we conclude that their stoichiometry is fixed at ∼Eu2.6Zn0.65Sn0.85As3, which meets the chemical charge balance. Eu3−δZn xSn yAs3 is composed of septuple (Eu1−δSn yAs2)-Eu-(Zn xAs)-Eu sequences. The shortest Eu–Eu distance in the system is between two Eu layers separated by Zn xAs along the c-axis. Magnetization measurement shows an antiferromagnetic ordering in Eu3−δZn xSn yAs3 at TN ∼ 12 K, where the magnetic easy-axis is along the c-axis, and Mössbauer spectroscopy observes magnetic hyperfine splitting on Eu and Sn at 6 K. Magnetic anisotropy is significantly different from the ones along the ab-plane in other layered Eu-based magnetic semimetals. Heat capacity measurements confirm the magnetic transition around 12 K. Electrical resistivity measurement indicates semiconductor behavior with a band gap of ∼0.86 eV. Various Eu-based magnetic semiconductors could provide a tunable platform to study potential topological and magnetic properties.

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Piccinelli, Fabio, Irene Carrasco, Chong-Geng Ma, Alok M. Srivastava i Marco Bettinelli. "Disorder-Induced Breaking of the Local Inversion Symmetry in Rhombohedral Pyrochlores M2La3Sb3O14(M = Mg or Ca): A Structural and Spectroscopic Investigation". Inorganic Chemistry 57, nr 15 (17.07.2018): 9241–50. http://dx.doi.org/10.1021/acs.inorgchem.8b01261.

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Thöle, Florian, i Nicola A. Spaldin. "Magnetoelectric multipoles in metals". Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences 376, nr 2134 (29.10.2018): 20170450. http://dx.doi.org/10.1098/rsta.2017.0450.

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In this paper, we demonstrate computationally the existence of magnetoelectric multipoles, arising from the second-order term in the multipole expansion of a magnetization density in a magnetic field, in non-centrosymmetric magnetic metals. While magnetoelectric multipoles have long been discussed in the context of the magnetoelectric effect in non-centrosymmetric magnetic insulators , they have not previously been identified in metallic systems, in which the mobile carriers screen any electrical polarization. Using first-principles density functional calculations, we explore three specific systems: first, a conventional centrosymmetric magnetic metal, Fe, in which we break inversion symmetry by introducing a surface, which both generates magnetoelectric monopoles and allows a perpendicular magnetoelectric response. Next, the hypothetical cation-ordered perovskite, SrCaRu 2 O 6 , in which we study the interplay between the magnitude of the polar symmetry breaking and that of the magnetic dipoles and multipoles, finding that both scale proportionally to the structural distortion. Finally, we identify a hidden antiferromultipolar order in the non-centrosymmetric, antiferromagnetic metal Ca 3 Ru 2 O 7 , and show that, while its competing magnetic phases have similar magnetic dipolar structures, their magnetoelectric multipolar structures are distinctly different, reflecting the strong differences in transport properties. This article is part of the theme issue ‘Celebrating 125 years of Oliver Heaviside's ‘Electromagnetic Theory’’.

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Wang, Dan, Cui-E. Hu, Li-Gang Liu, Min Zhang i Xiang-Rong Chen. "An Efficient Dopant for Introducing Magnetism into Topological Insulator Bi2Se3". Materials 15, nr 11 (28.05.2022): 3864. http://dx.doi.org/10.3390/ma15113864.

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In this work, we obtained an effective way to introduce magnetism into topological insulators, and successfully fabricated single crystal C-Bi2Se3. The structural, electrical and magnetic properties of non-magnetic element X (B, C and N) doped at Bi, Se1, Se2 and VDW gap sites of Bi2Se3 were studied by the first principles. It is shown that the impurity bands formed inside the bulk inverted energy gap near the Fermi level with C doping Bi2Se3. Due to spin-polarized ferromagnetic coupling, the time inversion symmetry of Bi2Se3 is destroyed. Remarkably, C is the most effective dopant because of the magnetic moment produced by doping at all positions. The experiment confirmed that the remnant ferromagnetism Mr is related to the C concentration. Theoretical calculations and experiments confirmed that carbon-doped Bi2Se3 is ferromagnetic, which provides a plan for manipulating topological properties and exploring spintronic applications.

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Zhang, Y. J., Z. H. Liu, Z. G. Wu i X. Q. Ma. "Prediction of fully compensated ferrimagnetic spin-gapless semiconducting FeMnGa/Al/In half Heusler alloys". IUCrJ 6, nr 4 (9.05.2019): 610–18. http://dx.doi.org/10.1107/s2052252519005062.

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Materials with full spin polarization that exhibit zero net magnetization attract great scientific interest because of their potential applications in spintronics. Here, the structural, magnetic and electronic properties of a C1 b -ordered FeMnGa alloy are reported using first-principles calculations. The results indicate that the corresponding band structure exhibits a considerable gap in one of the spin channels and a zero gap in the other thus allowing for high mobility of fully spin-polarized carriers. The localized magnetic moments of Fe and Mn atoms have an antiparallel arrangement leading to fully compensated ferrimagnetism, which possesses broken magnetic inversion symmetry. Such magnetic systems do not produce dipole fields and are extremely stable against external magnetic fields. Therefore, this will improve the performance of spintronic devices. Using this principle, similar band dispersion and compensated magnetic moments were predicted in a C1 b -ordered FeMnAl0.5In0.5 Heusler alloy.

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Friedrichs, Steffi, i Peter G. Jones. "Secondary Interactions in Gold(I) Complexes with Thione Ligands. 2. Three Ionic Camphorsulfonates with Z’ = 2 [1]". Zeitschrift für Naturforschung B 59, nr 7 (1.07.2004): 793–9. http://dx.doi.org/10.1515/znb-2004-0708.

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All three structures of the form bis(thione)gold(I) camphor-10-sulfonate [thione = imidazolidine-2-thione, 1; 1-methyl-imidazolidine-2-thione, 2; thiazolidine-2-thione, 3] crystallize in chiral space groups with Z′ = 2; local inversion symmetry of the cationic assemblies (less pronounced for 3) provides some rationalisation for this. The basic structural units are accounted for in terms of classical hydrogen bonds, leading to rings involving ion pairs for 1 and 2, but to infinite chains of anions and cations for 3. Neighbouring ion pairs in 1 are joined by further classical hydrogen bonds, in 2 via interactions between parallel S-Au-S axes. Other interactions include Au···N for 1, Au···S and Au···O for 3, and weak hydrogen bonds C-H···O and C-H···S, especially between adjacent chains in 3. Each structure is divided into hydrophobic and hydrophilic regions.

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Orlov, Dmitriy S., Olga V. Shamova, Igor E. Eliseev, Maria S. Zharkova, Oleg B. Chakchir, Nikolinka Antcheva, Sotir Zachariev i in. "Redesigning Arenicin-1, an Antimicrobial Peptide from the Marine Polychaeta Arenicola marina, by Strand Rearrangement or Branching, Substitution of Specific Residues, and Backbone Linearization or Cyclization". Marine Drugs 17, nr 6 (23.06.2019): 376. http://dx.doi.org/10.3390/md17060376.

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Arenicin-1, a β-sheet antimicrobial peptide isolated from the marine polychaeta Arenicola marina coelomocytes, has a potent, broad-spectrum microbicidal activity and also shows significant toxicity towards mammalian cells. Several variants were rationally designed to elucidate the role of structural features such as cyclization, a certain symmetry of the residue arrangement, or the presence of specific residues in the sequence, in its membranolytic activity and the consequent effect on microbicidal efficacy and toxicity. The effect of variations on the structure was probed using molecular dynamics simulations, which indicated a significant stability of the β-hairpin scaffold and showed that modifying residue symmetry and β-strand arrangement affected both the twist and the kink present in the native structure. In vitro assays against a panel of Gram-negative and Gram-positive bacteria, including drug-resistant clinical isolates, showed that inversion of the residue arrangement improved the activity against Gram-negative strains but decreased it towards Gram-positive ones. Variants with increased symmetry were somewhat less active, whereas both backbone-cyclized and linear versions of the peptides, as well as variants with R→K and W→F replacement, showed antimicrobial activity comparable with that of the native peptide. All these variants permeabilized both the outer and the inner membranes of Escherichia coli, suggesting that a membranolytic mechanism of action was maintained. Our results indicate that the arenicin scaffold can support a considerable degree of variation while maintaining useful biological properties and can thus serve as a template for the elaboration of novel anti-infective agents.

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McCabe, Emma E., Hai L. Feng, Chang-Jong Kang, Pascal Manuel, Fabio Orlandi, Yu Su, Jie Chen i in. "Pb₂NiOsO₆: antiferromagnetic order breaks inversion symmetry in high-pressure perovskite". Acta Crystallographica Section A Foundations and Advances 77, a2 (14.08.2021): C405. http://dx.doi.org/10.1107/s0108767321092813.

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Arman, Hadi D., Pavel Poplaukhin i Edward R. T. Tiekink. "An unprecedented binuclear cadmium dithiocarbamate adduct: bis[μ2-N-(2-hydroxyethyl)-N-isopropylcarbamodithioato-κ3S:S,S′]bis{[N-(2-hydroxyethyl)-N-isopropylcarbamodithioato-κ2S,S′](3-{(1E)-[(E)-2-(pyridin-3-ylmethylidene)hydrazin-1-ylidene]methyl}pyridine-κN)cadmium]} dihydrate". Acta Crystallographica Section E Crystallographic Communications 72, nr 9 (2.08.2016): 1234–38. http://dx.doi.org/10.1107/s2056989016012214.

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The asymmetric unit in the title binuclear compound, [Cd(C6H12NOS2)2(C12H10N4)]2·2H2O, comprises a CdIIatom, two dithiocarbamate (dtc) anions, a monodentate 3-pyridinealdazine ligand and a lattice water molecule. The binuclear molecule is constructed by the application of inversion symmetry. One dtc ligand simultaneously chelates one cadmium atom and bridges the centrosymmetric mate, while the other dtc ligand is chelating only. This leads to a centrosymmetric [Cd(dtc)2]2core to which are appended two 3-pyridinealdazine ligands. The resulting NS5donor set is based on an octahedron. The three-dimensional molecular packing is sustained by hydroxyl-O—H(hydroxyl) and water-O—H...O(hydroxyl) hydrogen bonding, leading to supramolecular layers parallel to (101) which are connected by water-O—H...N(pyridyl) hydrogen bonding; additional C—H...O, S π(chelate ring) interactions are also evident. The retention of the central [Cd(dtc)2]2core upon adduct formation is unprecedented in the structural chemistry of the zinc-triad dithiocarbamates.

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