Orbital density wave induced by electron-lattice coupling in orthorhombic iron pnictides

In this paper we explore the magnetic and orbital properties closely related to a tetragonal-orthorhombic structural phase transition in iron pnictides based on both two- and five-orbital Hubbard models. The electron-lattice coupling, which interplays with electronic interaction, is self-consistently treated. Our results reveal that the orbital polarization stabilizes the spin density wave (SDW) order in both tetragonal and orthorhombic phases. However, the ferro-orbital density wave (F-ODW) only occurs in the orthorhombic phase rather than in the tetragonal one. Magnetic moments of Fe are small in the intermediate Coulomb interaction region for the striped antiferromangnetic phase in the realistic five orbital model. The anisotropic Fermi surface in the SDW/ODW orthorhombic phase is well in agreement with the recent angle-resolved photoemission spectroscopy experiments. These results suggest a scenario that the magnetic phase transition is driven by the ODW order mainly arising from the electron-lattice coupling.Comment: 21 pages, 10 figure

Modified Hertz-damp model for base-isolated structural pounding simulation under near-fault earthquakes

Pounding phenomenon between base-isolated structures under near-fault earthquakes has been widely investigated with various impact models around the world. Firstly, the existing impact analysis models are summarized and discussed in this paper. For the Hertz-damp impact model, the damping constant does not coincide with its physical fact. Then, the damping constant in the Hertz-damp impact analysis model was modified based on the Hertz theory. Next, the approximate formula of the damping constant is theoretically derived, and the effectiveness is verified by a simulation analysis. The numerical results show that the pounding can significantly increase the floor acceleration, especially at the isolation layer. In addition, the impact stiffness has a significant effect on the acceleration response, and the inter-story drifts are also sensitive to the variety of impact stiffness. The simulation results indicate that excessive flexibility at the base-isolated system may lead to a susceptible pounding with a limited seismic gap

Tetra­kis(μ-naphthalene-1-acetato-1:2κ2 O:O′)bis­(naphthalene-1-acetato)-1κ2 O,O′;2κ2 O,O′-bis­(1,10-phenanthroline)-1κ2 N,N′;2κ2 N,N′-europium(III)samarium(III)

In the title compound, [EuSm(C12H9O2)6(C12H8N2)2], the metal site is statistically occupied (50:50) by Eu and Sm atoms, forming a centrosymmetric complex. The metal site is nine-coordinate, in a distorted monocapped square-anti­prismatic coordination geometry. Mol­ecules are linked into three chains by C—H⋯π interactions and C—H⋯O hydrogen bonds. The combination of these chains generates a three-dimensional framework structure. One of the bridging naphthalene-1-ace­tate ligands was found to be disordered over two sites; the site occupancies for the naphthylmethyl group refined to 0.628 (14) and 0.372 (14)

Diaqua­bis(N,N′-dibenzyl­ethane-1,2-diamine-κ2 N,N′)nickel(II) dichloride N,N-dimethyl­formamide solvate

The asymmetric unit of the title complex, [Ni(C16H20N2)2(H2O)2]Cl2·C3H7NO, consists of two NiII atoms, each lying on an inversion center, two Cl anions, two N,N′-dibenzyl­ethane-1,2-diamine ligands, two coordinated water mol­ecules and one N,N-dimethyl­formamide solvent mol­ecule. Each NiII atom is six-coordinated in a distorted octa­hedral coordination geometry, with the equatorial plane formed by four N atoms and the axial positions occupied by two water mol­ecules. The complex mol­ecules are linked into a chain along [001] by N—H⋯Cl, N—H⋯O and O—H⋯Cl hydrogen bonds. The C atoms and H atoms of the solvent mol­ecule are disordered over two sites in a ratio of 0.52 (2):0.48 (2)

Bis{6,6′-dimeth­oxy-2,2′-[ethane-1,2-diyl­bis(imino­methyl­ene)]diphenolato(1.5−)-κ4 O,N,N′,O′}praeseodymium(III)

The title compound, [Pr(C18H22.5N2O4)2], is isotypic with its Er and Tb analogues. All interatomic distances, angles and the hydrogen bond geometry are very similar for the three structures.

Bis{6,6′-dimeth­oxy-2,2′-[ethane-1,2-diyl­bis(imino­methyl­ene)]diphenolato(1.5−)-κ4 O,N,N′,O′}terbium(III)

The title compound, [Tb(C18H22.5N2O4)2], is isotypic with its Pr and Tb analogues. All interatomic distances, angles and the hydrogen bond geometry are very similar for the three structures

Poly[(N,N-dimethyl­formamide-κO)tris­(μ-naphthalene-1-acetato)terbium(III)]

In title compound, [Tb(C12H9O2)3(C3H7NO)]n, the Tb atom is nine-coordinated by nine O atoms from three naphthalene-1-acetate and one N,N-dimethyl­formamide ligands. The Tb atoms are linked by three bridging naphthalene-1-acetate ligands into a chain parallel to the b axis. Further stabilization of the structure is accomplished by non-classical C—H⋯O hydrogen bonds and C—H⋯π interactions