For Li 2 FeSiO 4 , its P2 1 space group makes it possibly perfect as a new cathode material for Li-ion batteries (Nishimura et al. J. Am. Chem. Soc. 2008, 130, 13212). For this type of Li 2 MSiO 4 (M ) Mn, Fe, and Co), the structural, electronic, and electrochemical properties have been investigated, using the density functional theory with the exchange-correlation energy treated as the generalized gradient approximation (GGA) plus on-site Coulomb energy correction (+U). Within the GGA+U framework, the fully lithiated Li 2 MSiO 4 as well as the delithiated LiMSiO 4 and MSiO 4 are all semiconducting, and the band gap lowers with the extraction of lithium ions. The fully lithiated compounds are all stabilized at their ferromagnetic phase, while the delithiated compounds are all stabilized when antiferromagnetic. Starting from the P2 1 structure, the fully delithiated MSiO 4 has better stability than that obtained from Pmn2 1 structure. In Li 2 FeSiO 4 , the possibility of reversibly extracting more than one lithium ion is enhanced because of the lower stability of the intermediate phase LiFeSiO 4 comparing with the Pmn2 1 symmetry situation. Li 2 MnSiO 4 with the P2 1 symmetry has higher electronic conductivity, and Li 2 CoSiO 4 has the suitable second-step voltage of less than 5.0 V. All Li 2 FeSiO 4 , Li 2 MnSiO 4 , and Li 2 CoSiO 4 are predicted as promising cathode materials.

By calculating orbitally resolved Pauli susceptibilities within maximally localized Wannier orbital basis transformed from first principles band structures, we find that magnetism in Fe1+xTe still has its itinerant origin even without Fermi surface nesting, provided orbital modulation of particle-hole excitations are considered. This leads to strong magnetic instabilities at wave vector (0,π)/(π,0) in dxz/dyz orbitals that are responsible for the bicollinear antiferromagnetic state as extra electrons donated from excess Fe are considered. Magnetic exchange coupling between excess Fe and in-plane Fe further stabilizes the bicollinear antiferromagnetic order. Our results reveal that magnetism and superconductivity in iron chalcogenides may have different orbital origin, as Pauli susceptibilities of different orbitals evolve differently as a function of concentration of excess Fe and height of the chalcogen atom measured from the iron plane.

The magnetic behaviors in Fe(Se,Te) systems have been investigated systematically using density functional calculations. At the experimental lattice parameters, the ground state is found to be in the double stripe magnetic phase for FeTe but in the single stripe magnetic phase for FeSe and FeSe0.5Te0.5, and there is no preference in the different easy axes of magnetization. Substitution of Se by Te enlarges the size of the Fermi surface in FeSe0.5Te0.5, resulting in a stronger nesting effect and thus enhancing the superconductivity. It is found that the double stripe order in FeTe1-xSex changes to the single stripe order when x> 0.18. Spiral calculations on FeSe0.5Te0.5 show that the lowest energy is at the commensurate point Q→= (0.5,0.5), accompanied by additional local minima at two incommensurate points near Q→= (0.5,0.5). This observation is consistent with the experimentally observed positions of low energy magnetic excitations. Geometry optimization calculations show that the tetragonal cell relaxes to orthorhombic and monoclinic cells for FeSe and FeTe, respectively, but remains unchanged for FeSe0.5Te0.5.

The electronic and magnetic properties of BaTi 2 As 2 O have been investigated using both the first-principles and analytical methods. The full-potential linearized augmented plane-wave calculations show that the most stable state is a site-selective antiferromagnetic (AFM) metal with a 2 × 1 × 1 magnetic unit cell containing two nonmagnetic Ti atoms and two other Ti atoms with antiparallel moments. Further analysis to Fermi surface and spin susceptibility shows that the site-selective AFM ground state is driven by the Fermi surface nesting and the Coulomb correlation. Meanwhile, the charge density distribution remains uniform, suggesting that the phase transition at 200 K in experiment is a spin-density-wave (SDW) transition.PACS numbers: 31.15. 75.10.Jm, 74.20Mn, 75.40.Cx

Incorporating the global production network approach and competitor analysis, this paper establishes an analytical framework with two hypotheses for the role of foreign multinational enterprises (FMNEs) in indigenous firms' exports and domestic sales. First, the presence of FMNEs as a whole is likely to have a negative impact on indigenous firms' domestic sales but a simultaneous positive impact on their exports in an emerging economy like China. Second, the presence of MNEs from Hong Kong, Macau and Taiwan (HMT MNEs) is more likely to generate this pattern of impact than MNEs from other countries (Other FMNEs). The FDI-led export strategy contributed to the dominance of the scenario described by the first hypothesis in China, while a higher degree of market commonality and resource similarity of HMT MNEs with that of indigenous Chinese firms than Other FMNEs leads to the second hypothesis. These novel hypotheses are tested and supported by a very large and recent firm-level panel dataset from Chinese manufacturing.