Search results for "Orbital"
showing 10 items of 679 documents
Effect of Metal Complexation on the Conductance of Single-Molecular Wires Measured at Room Temperature
2014
The present work aims to give insight into the effect that metal coordination has on the room-temperature conductance of molecular wires. For that purpose, we have designed a family of rigid, highly conductive ligands functionalized with different terminations (acetylthiols, pyridines, and ethynyl groups), in which the conformational changes induced by metal coordination are negligible. The single-molecule conductance features of this series of molecular wires and their corresponding Cu(I) complexes have been measured in break-junction setups at room temperature. Experimental and theoretical data show that no matter the anchoring group, in all cases metal coordination leads to a shift towar…
Electron Spin Resonance study of charge trapping in α-ZnMoO4 single crystal scintillator
2015
The origin and properties of electron and hole traps simultaneously appearing in a-ZnMoO4 scintillator after X-ray irradiation at low temperatures (T < 35 K) were studied by Electron Spin Resonance (ESR). ESR spectrum of the electron type trap shows pronounced superhyperfine structure due to the interaction of electron spin with nuclear magnetic moments of 95,97Mo and 67Zn lattice nuclei. Considering the nearly tetragonal symmetry of the center this allows us to identify the electron trap as an electron self-trapped at the (Mo(1)O4) 2 complex. Nearly 60% reduction of the spin–orbit coupling at the Mo(1) ion is caused by the overlap of the Mo and ligand oxygen orbitals indicating an essentia…
Efficient Linear-Scaling Density Functional Theory for Molecular Systems
2013
Despite recent progress in linear scaling (LS) density function theory (DFT), the computational cost of the existing LS methods remains too high for a widespread adoption at present. In this work, we exploit nonorthogonal localized molecular orbitals to develop a series of LS methods for molecular systems with a low computational overhead. High efficiency of the proposed methods is achieved with a new robust two-stage variational procedure or by replacing the optimization altogether with an accurate nonself-consistent approach. We demonstrate that, even for challenging condensed-phase systems, the implemented LS methods are capable of extending the range of accurate DFT simulations to molec…
Intermolecular oxidative dehydrogenative 3,3′-coupling of benzo[b]furans and benzo[b]thiophenes promoted by DDQ/H+: total synthesis of shandougenine B
2016
With an excess of a strong acid, 2,3-dichloro-5,6-dicyano-1,4-quinone (DDQ) is shown to promote metal-free intermolecular oxidative dehydrogenative (ODH) 3,3'-coupling of 2-aryl-benzo[b]furans and 2-aryl-benzo[b]thiophenes up to 92% yield as demonstrated with 9 substrates. Based on the analysis of oxidation potentials and molecular orbitals combined with EPR, NMR and UV-Vis observations, the studied reaction is initiated by a DDQ-substrate charge transfer complex and presumably proceeds via oxidation of the substrate into an electrophilic radical cation that further reacts with another molecule of a neutral substrate. The coupling reactivity can easily be predicted from the oxidation potent…
Wind accretion in the massive X-ray binary 4U 2206+54: abnormally slow wind and a moderately eccentric orbit
2006
Massive X-ray binaries are usually classified depending on the properties of the donor star in classical, supergiant and Be X-ray binaries. The massive X-ray binary 4U 2206+54 does not fit in any of these groups, and deserves a detailed study to understand how the transfer of matter and the accretion on to the compact object take place. To this end we study an IUE spectrum of the donor and obtain a wind terminal velocity (v_inf) of ~350 km/s, which is abnormally slow for its spectral type. We also analyse here more than 9 years of available RXTE/ASM data. We study the long-term X-ray variability of the source and find it to be similar to that observed in the wind-fed supergiant system Vela …
Posttraumatic carotid-cavernous fistula: Pathogenetic mechanisms, diagnostic management and proper treatment. A case report.
2016
Journal Article; UNLABELLED Carotid-cavernous fistulas are an uncommon diseases characterized by abnormal communications between arteries and veins located in the cavernous sinus. According with Barrow´s classification they could be divided in two groups: direct and indirect. The typical symptoms showed by theses pathologies are: pulsating exophthalmos and orbital blow. The present study describes a case of direct posttraumatic carotid-cavernous fistula in a 26 years old man. Furthermore, we present the images that we used to make the diagnosis. In this light, we decided to treat this case with endovascular approach after considering several therapeutic options. The aim of the present repor…
Measurement of spin-orbital angular momentum interactions in relativistic heavy-ion collisions
2020
The first evidence of spin alignment of vector mesons ($K^{*0}$ and $\phi$) in heavy-ion collisions at the Large Hadron Collider (LHC) is reported. The spin density matrix element $\rho_{00}$ is measured at midrapidity ($|y| <$ 0.5) in Pb-Pb collisions at a center-of-mass energy ($\sqrt{s_{\rm NN}}$) of 2.76 TeV with the ALICE detector. $\rho_{00}$ values are found to be less than 1/3 (1/3 implies no spin alignment) at low transverse momentum ($p_{\rm T} <$ 2 GeV/$c$) for $K^{*0}$ and $\phi$ at a level of 3$\sigma$ and 2$\sigma$, respectively. No significant spin alignment is observed for the $K^0_S$ meson (spin = 0) in Pb-Pb collisions and for the vector mesons in $pp$ collisions. The meas…
Ab initio calculations of pure and Co+2-doped MgF2 crystals
2020
This research was partly supported by the Kazakhstan Science Project № AP05134367«Synthesis of nanocrystals in track templates of SiO2/Si for sensory, nano- and optoelectronic applications», as well as by Latvian Research Council project lzp-2018/1-0214. Calculations were performed on Super Cluster (LASC) in the Institute of Solid State Physics (ISSP) of the University of Latvia. Authors are indebted to S. Piskunov for stimulating discussions.
Vertical spectrum of ethene: uncontracted versus contracted correlation methods and the role of the adapted molecular orbitals
1998
Abstract Ethylene vertical excitation energies (VEE) below 9.5 eV have been calculated with the complete active-space singles and doubles configuration interaction self-consistent size-consistent dressing (SC) 2 CAS–SDCI. The mean of the absolute deviation from experiment for the calculated VEE are 0.14, 0.05 and 0.03 eV for three different molecular orbital (MO) sets tried. The results show that an uncontracted method and a realistic MO set avoid the difficulties present in the calculation of the strongly mixed Rydberg-valence 1B 1u states.
External pressure and composition effects on the atomic and electronic structure of SnWO4
2015
The atomic and electronic structure of tin tungstates, α-SnWO4, α-Sn1.03W0.99O4 and β-SnWO4 ,w as studied by the W L3-edge X-ray absorption spectroscopy and first-principles linear combination of atomic orbital (LCAO) calculations based on the hybrid exchange-correlation density functional (DFT)/ Hartree–Fock (HF) scheme. It was found that the crystal structure of both α-phases is built up of strongly distorted WO6 octahedra, whereas that of β-SnWO4 is composed of nearly regular WO4 tetrahedra. In addition, there are distorted SnO6 octahedra in both α- and β-phases. The metal–oxygen octahedra distortion is explained by the second-order Jahn–Teller effect. The influence of pressure on the st…