Unfolding first-principles band structures

A general method is presented to unfold band structures of first-principles super-cell calculations with proper spectral weight, allowing easier visualization of the electronic structure and the degree of broken translational symmetry. The resulting unfolded band structures contain additional rich information from the Kohn-Sham orbitals, and absorb the structure factor that makes them ideal for a direct comparison with angular resolved photoemission spectroscopy experiments. With negligible computational expense via the use of Wannier functions, this simple method has great practical value in the studies of a wide range of materials containing impurities, vacancies, lattice distortions, or spontaneous long-range orders.Comment: 4 pages, 3 figure

Dynamical Linear Response of TDDFT with LDA+U Functional: strongly hybridized Frenkel excitons in NiO

Within the framework of time-dependent density-functional theory (TDDFT), we derive the dynamical linear response of LDA+U functional and benchmark it on NiO, a prototypical Mott insulator. Formulated using real-space Wannier functions, our computationally inexpensive framework gives detailed insights into the formation of tightly bound Frenkel excitons with reasonable accuracy. Specifically, a strong hybridization of multiple excitons is found to significantly modify the exciton properties. Furthermore, our study exposes a significant generic limitation of adiabatic approximation in TDDFT with hybrid functionals and in existing Bethe-Salpeter-equation approaches, advocating the necessity of strongly energy-dependent kernels in future development.Comment: 5 pages, 2 figure

Unified Picture for Magnetic Correlations in Iron-Based Superconductors

The varying metallic antiferromagnetic correlations observed in iron-based superconductors are unified in a model consisting of both itinerant electrons and localized spins. The decisive factor is found to be the sensitive competition between the superexchange antiferromagnetism and the orbital-degenerate double-exchange ferromagnetism. Our results reveal the crucial role of Hund's rule coupling for the strongly correlated nature of the system and suggest that the iron-based superconductors are closer kin to manganites than cuprates in terms of their diverse magnetism and incoherent normal-state electron transport. This unified picture would be instrumental for exploring other exotic properties and the mechanism of superconductivity in this new class of superconductors.Comment: Revised for publication. 3 figure

EFFECT OF SHOULDER STRENGTH ON THE FLIGHT DISTANCE IN THE STANDING LONG JUMP

The purpose of this study was to identify the effect of different maximum shoulder joint force to the standing long jump distance. A five-segment model connected by frictionless hinge joints in plane motion was established for simulating the flight phase, and was driven by joint torques. The results show that jump distances are generally linearly related to maximum shoulder joint torque from 20 to 160 Nm. Further increase in shoulder joint strength fails to enhance the performance. Furthermore, a complete model combining both the ground contact and flight phases of the standing long jump should be used in future studies

3,3′-Bis(3-methoxy­benz­yl)-1,1′-ethyl­enediimidazolium dibromide

In the title compound, C24H28N4O2 2+·2Br−, the imidazolium cation is located on an inversion centre. The two imidazole rings are parallel to each other, whereas the imidazole and benzene rings make a dihedral angle of 77.25 (16)°. Non­classical inter­molecular C—H⋯Br hydrogen bonds link the imidazolium cations and the bromide anions into a three-dimensional network