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Lie symmetry

Guo-Jin Cao
Recently, the T-Hg(ii)2 -A base pair containing two equivalents of Hg(ii) has been prepared and characterized experimentally, which implies that there might exist considerable stable metal-mediated base pairs holding two neighbouring metal centers. Here we report a quantum chemical study on geometries, electronic structures, and bonding of various G2 Cu2 4+ (G = guanine) isomers including one di-copper(i) unit. Different density functional methods [Becke 3-parameter-Lee-Yang-Parr, Perdew-Becke-Ernzerhof, Becke-Perdew, Density Functional Theory with Dispersion Corrections (DFT-D)] assign ambiguous relative energies to these isomers with the singlet and triplet states...
October 14, 2018: Journal of Chemical Physics
Yukio Watanabe
In the calculations of tetragonal BaTiO3 , some exchange-correlation (XC) energy functionals such as local density approximation (LDA) have shown good agreement with experiments at room temperature (RT), e.g., spontaneous polarization ( P S ), and superiority compared with other XC functionals. This is due to the error compensation of the RT effect and, hence, will be ineffective in the heavily strained case such as domain boundaries. Here, ferroelectrics under large strain at RT are approximated as those at 0 K because the strain effect surpasses the RT effects...
May 21, 2018: Journal of Chemical Physics
T Peppler, P Dyke, M Zamorano, I Herrera, S Hoinka, C J Vale
We present an experimental investigation of collective oscillations in harmonically trapped Fermi gases through the crossover from two to three dimensions. Specifically, we measure the frequency of the radial monopole oscillation or breathing mode in highly oblate gases with tunable interactions. The breathing mode frequency is set by the adiabatic compressibility and probes the thermodynamic equation of state. In 2D, a dynamical scaling symmetry for atoms interacting via a δ potential predicts the breathing mode to occur at exactly twice the harmonic confinement frequency...
September 21, 2018: Physical Review Letters
B Mehnen, R Linguerri, S Ben Yaghlane, M Mogren Al Mogren, M Hochlaf
The ethynyl cation, C2H+, is of great importance in astrophysical media and in combustion. It is involved in the formation of larger organic compounds and in their decomposition mechanisms. Here, we investigate the low-lying electronic states of this cation using pure ab initio methodologies. The evolution of its potential energy surfaces along the stretching and bending coordinates reveals a high density of electronic states that favours mutual interactions and the mixing of wavefunctions. The ground state is of 3Π space symmetry and the lowest singlet state (1Π) is found to be a quasi-linear-quasi-linear Renner-Teller system...
September 20, 2018: Faraday Discussions
Sofia Canola, Juan Casado, Fabrizia Negri
A peculiar characteristic of open-shell singlet diradical molecules is the presence of a double exciton state (H,H → L,L) among low lying excited states. Recent high-level quantum-chemical investigations including a static and dynamic electron correlation have demonstrated that this state can become the lowest singlet excited state, a diagnostic fingerprint of the diradical system. Here we investigate the performance of less computationally demanding TDDFT calculations by employing two approaches: the spin-flip TDDFT scheme and TD calculations based on unrestricted broken symmetry antiparallel-spin reference configuration (TDUDFT)...
October 7, 2018: Physical Chemistry Chemical Physics: PCCP
Dan Zhou, Guoliang Li, Kevin B Moore, Yaoming Xie, Kirk A Peterson, Henry F Schaefer
Various types of hydrogen bonds have been recognized during the past century. In this research, a new type of noncovalent interaction, the dipole-induced hydrogen bond formed between a hydrogen molecule and an alkali halide, H-H···F-M, is studied. Proposed by Zhang and co-workers ( Phys. Chem. Chem. Phys. 2015, 17, 20361), these systems are extensively investigated initially using the "gold standard" CCSD(T) method in conjunction with augmented correlation-consistent polarized core-valence basis sets up to quadruple-ζ...
October 9, 2018: Journal of Chemical Theory and Computation
Eduardo Martin-Lopez, Sarah J Meller, Charles A Greer
The anterior commissure (AC) is a phylogenetically conserved inter-hemispheric connection found among vertebrates with bilateral symmetry. The AC connects predominantly olfactory areas but many aspects of its development and structure are unknown. To fill this gap, we investigated the embryonic and postnatal development of the AC by tracing axons with DiI and the piggyback transposon multicolor system. With this strategy, we show that axon growth during establishment of the AC follows a strictly regulated timeline of events that include waiting periods ("regressive strategies") as well as periods of active axon outgrowth ("progressive strategies")...
August 24, 2018: Brain Structure & Function
Mariusz Tasior, Khaled Hassanein, Leszek M Mazur, Ioanna Sakellari, David Gray, Maria Farsari, Marek Samoć, Fabrizio Santoro, Barbara Ventura, Daniel T Gryko
A three-step synthetic route to a structurally unique π-expanded pyrrolo[3,2-b]pyrrole derived bis-ketone has been developed. In contrast to all previous ladder-type pyrrolopyrroles, the new dye exhibits a low-energy absorption band in the visible region which is responsible for its red-purple color. Interestingly, even though the compound is centrosymmetric, this band coincides with the lowest energy two-photon absorption (TPA) transition. This non-typical behaviour has been computationally rationalized by finding two close lying excited states, one of which (S1) is active for OPA and the other (S2) for TPA processes, which arise from the mixing of two symmetric partial charge-transfer states...
August 29, 2018: Physical Chemistry Chemical Physics: PCCP
Christiane Binot, Jean-François Sadoc, Claude-Henri Chouard
Liquid crystals (LC) are an intermediate state between an ordered crystalline solid and a more disordered liquid. LCs (or mesophases) are ubiquitous in living systems, optimizing multiple biological functions that could not operate in purely solid or liquid environments as both mobility and organization are needed. One of us recently suggested that there is an information vector, shared by neurodegenerative and infectious pathologies, to be found within lipid rafts in an ordered liquid (Lo) form mediated by cholesterol...
July 2018: Heliyon
Joseph P Heindel, Elizabeth S Knodel, Daniel P Schofield
We have demonstrated the application of many-body expansions to calculations of the anharmonic, local-mode, OH-stretching vibrational frequencies of water clusters. We focused on five low-lying isomers of the water hexamer and the DD*(20,1) isomer of (H2 O)21 . Our approach provides accurate OH-stretching vibrational frequencies when treating one- and two-body interactions with the CCSD(T)-F12 level of theory and the three- and four-body interactions with the DF-MP2-F12 level. Additionally, we have investigated the physical origin of the large contribution that two- and three-body interactions make to the shifts of vibrational frequencies using symmetry-adapted perturbation theory (SAPT)...
August 23, 2018: Journal of Physical Chemistry. A
M E Sasin, A G Smolin, K-H Gericke, E Tokunaga, O S Vasyutinskii
This paper presents the detailed study of two-photon excited fluorescence in indole dissolved in propylene glycol produced by two-photon absorption from the molecular ground state to several high lying excited states. The experimental method involved excitation with linearly and circularly polarized femtosecond pulses and time-resolved detection of the polarized fluorescence decay. The fluorescence intensity, anisotropy, excited state lifetime, and rotation diffusion time as function of the excitation light wavelength in the spectral range 385-510 nm were determined in experiment...
August 1, 2018: Physical Chemistry Chemical Physics: PCCP
Joy Christian
The exceptional Lie group E 8 plays a prominent role in both mathematics and theoretical physics. It is the largest symmetry group associated with the most general possible normed division algebra, namely, that of the non-associative real octonions, which-thanks to their non-associativity-form the only possible closed set of spinors (or rotors) that can parallelize the 7-sphere. By contrast, here we show how a similar 7-sphere also arises naturally from the algebraic interplay of the graded Euclidean primitives, such as points, lines, planes and volumes, which characterize the three-dimensional conformal geometry of the ambient physical space, set within its eight-dimensional Clifford-algebraic representation...
May 2018: Royal Society Open Science
Christopher P Gordon, Satoru Shirase, Keishi Yamamoto, Richard A Andersen, Odile Eisenstein, Christophe Copéret
d0 metal-alkyl complexes (M = Ti, Zr, and Hf) show specific activity and selectivity in olefin polymerization and oligomerization depending on their ligand set and charge. Here, we show by a combined experimental and computational study that the 13 C NMR chemical shift tensors of the α-carbon of metal alkyls that undergo olefin insertion signal the presence of partial alkylidene character in the metal-carbon bond, which facilitates this reaction. The alkylidene character is traced back to the π-donating interaction of a filled orbital on the alkyl group with an empty low-lying metal d-orbital of appropriate symmetry...
June 26, 2018: Proceedings of the National Academy of Sciences of the United States of America
Davide Delmonte, Claudia Gori, Erica Lambruschi, Luciana Mantovani, Francesco Mezzadri, Danilo Bersani, Pier Paolo Lottici, Edmondo Gilioli, Massimo Solzi, Mario Tribaudino
We report a detailed study on the magnetic properties of the pyroxene series M2M1Si2 O6 , with M2  =  Ca and M1  =  Mg, where magnesium and then calcium are progressively substituted by cobalt. For cobalt site occupancy larger than 0.7 at the M1 site, a collinear antiferromagnetic phase is detected for T  <  T N1   =  12 K with a monodimensional character (i.e. M1 site intra-chain order parallel to c axis). Moreover the magnetization easy axis has been estimated to lie roughly along the [1 0 1] direction...
July 18, 2018: Journal of Physics. Condensed Matter: An Institute of Physics Journal
Nadir Ghichi, Ali Benboudiaf, Yacine DJebli, Chawki Bensouici, Hocine Merazig
The whole mol-ecule of the title Schiff base compound, C34 H28 N2 O4 , is generated by mirror symmetry, with the mirror bis-ecting the central benzene ring. It was synthesized via the condensation reaction of 1,2-di-amine-benzene with 4-benz-yloxy-2-hy-droxy-benzaldehyde. The mol-ecule is V-shaped and there are two intra-molecular O-H⋯N hydrogen bonds present forming S (6) ring motifs. The configuration about the C=N imine bonds is E . The central benzene ring makes dihedral angles of 41.9 (2) and 43.6 (2)° with the phenol ring and the outer benz-yloxy ring, respectively...
May 1, 2018: Acta Crystallographica. Section E, Crystallographic Communications
Sandra Fusco, Angela Tuzi, Roberto Centore, Antonio Carella
Mol-ecules of the title compound, C24 H8 F4 N2 O8 , have C i point-group symmetry in the crystal, as they lie on crystallographic inversion centres ( Z ' = 1/2). The di-fluoro-phenyl ring is disordered over two orientations; the final refined occupancy factors of the two components of disorder are 0.947 (4) and 0.053 (4). In the crystal, some Car -H⋯F inter-actions are present, which involve the most acidic H atom of the mol-ecule.
February 1, 2018: Acta Crystallographica. Section E, Crystallographic Communications
Raphael F Ribeiro, Joel Yuen-Zhou
Explorations of the consequences of the Jahn-Teller (JT) effect remain active in solid-state and chemical physics. In this topical review we revisit the class of JT models which exhibit continuous vibronic symmetries. A treatment of these systems is given in terms of their algebraic properties. In particular, the compact symmetric spaces corresponding to JT models carrying a vibronic Lie group action are identified, and their invariants used to reduce their adiabatic potential energy surfaces into orbit spaces of the corresponding Lie groups...
August 22, 2018: Journal of Physics. Condensed Matter: An Institute of Physics Journal
Duo Lin, Tianxun Gong, Zi-Yao Hong, Sufang Qiu, Jianji Pan, Chinh-Yu Tseng, Shangyuan Feng, Rong Chen, Kien Voon Kong
By taking advantage of the spectral properties of metal carbonyls, we have designed a surface-enhanced Raman spectroscopy (SERS) ratiometric assay for measuring cell-free circulating DNA (cfDNA) from Epstein-Barr virus in blood for nasopharyngeal carcinoma (NPC). This assay consists of a rhenium carbonyl (Re-CO) to serve as a DNA probe, an osmium carbonyl (Os-CO) embedded within the SERS-active substrate as an internal reference, and a streptavidin layer on the surface of the substrate. Hybridization of cfDNA with biotinylated-capture sequence leads to immobilization of cfDNA on the substrate...
June 19, 2018: Analytical Chemistry
Vivek Kumar, Manfred Reehuis, Andreas Hoser, Peter Adler, Claudia Felser
We have investigated the crystal and magnetic structure of Mn2 PtPd alloy using powder x-ray and neutron diffraction experiments. This compound is believed to belong to the Heusler family having crystal symmetry I4/mmm (TiAl3 -type). However, in this work we found that the Pd and Pt atoms are disordered and thus Mn2 PtPd crystallizes in the L10 structure having P4/mmm symmetry (CuAu-I type) like MnPt and MnPd binary alloys. The lattice constants are a  =  2.86 Å and c  =  3.62 Å at room temperature...
July 4, 2018: Journal of Physics. Condensed Matter: An Institute of Physics Journal
Heli K Hyytiäinen, Sari H Mölsä, Jouni J T Junnila, Outi M Laitinen-Vapaavuori, Anna K Hielm-Björkman
This study aimed at developing a quantitative testing battery for dogs' stifle functionality, as, unlike in human medicine, currently none is available in the veterinary field. Forty-three dogs with surgically treated unilateral cranial cruciate ligament rupture and 21 dogs with no known musculoskeletal problems were included. Eight previously studied tests: compensation in sitting and lying positions, symmetry of thrust in hindlimbs when rising from lying and sitting, static weight bearing, stifle flexion and extension and muscle mass symmetry, were summed into the Finnish Canine Stifle Index (FCSI)...
September 15, 2018: Veterinary Record
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