In the original paper, figure 12(b) was incorrect and the caption of figure 12 was also erroneous. The correct figure and caption are shown below. E/t Figure 12. LDOS at the impurity site ρ 0A (top), the NN site ρ 0B (middle) and the next-NN site ρ 1A (bottom) obtained from equations (13) and (14) for different strengths of the impurity potential U 0 /t = 0, 2 and 5, denoted by black dashed, black solid and red dashed lines, respectively. As U 0 → ∞, the top LDOS goes to zero (except for the bound state beyond the top of the band whose energy goes to ∞), and the zero-mode state lives only on the B sublattice, as indicated from the middle and the bottom panels. The prominent zero-mode peak in the middle panel for U 0 /t = 5 will develop into a δ-function peak at E = 0 as the impurity potential U 0 → ∞.Abstract. We study the electronic structure of graphene with a single substitutional vacancy using a combination of the density-functional, tight-binding and impurity Green's function approaches. Density-functional studies are performed with the all-electron spin-polarized linear augmented plane wave (LAPW) method. The three sp 2 σ dangling bonds adjacent to the vacancy introduce localized states (Vσ ) in the mid-gap region, which split due to the crystal field and a Jahn-Teller distortion, while the p z π states introduce a sharp resonance state (Vπ ) in the band structure. For a planar structure, symmetry strictly forbids hybridization between the σ and the π states, so that these bands are clearly identifiable in the calculated band structure. As to the magnetic moment of the vacancy, the Hund's rule coupling aligns the spins of the four localized Vσ 1 ↑↓, Vσ 2 ↑ and Vπ ↑ electrons, resulting in an S = 1 state, with a magnetic moment of 2µ B , which is reduced by about 0.3µ B due to the anti-ferromagnetic spin polarization of the π band itinerant states in the vicinity of the vacancy. This results in the net magnetic moment of 1.7µ B . Using the Lippmann-Schwinger equation, we reproduce the well-known ∼1/r decay of the localized Vπ wave function with distance, and in addition, find an

In this paper we have applied the full-potential linearized muffin tin orbital method and the tight-binding linearized muffin tin orbital method to investigate in detail the electronic structure and magnetism of a series of half-Heusler compounds XMZ with X = Fe, Co, Ni, M = Ti, V, Nb, Zr, Cr, Mo, Mn and Z = Sb, Sn. Our detailed analysis of the electronic structure using various indicators of chemical bonding suggests that covalent hybridization of the higher-valent transition element X with the lower-valent transition element M is the key interaction responsible for the formation of the d-d gap in these systems. However, the presence of the sp-valent element is crucial to provide stability to these systems. The influence of the relative ordering of the atoms in the unit cell on the d-d gap is also investigated. We have also studied in detail some of these systems with more than 18 valence electrons which exhibit novel magnetic properties, namely half-metallic ferro-and ferrimagnetism. We show that the d-d gap in the paramagnetic state, the relatively large X-Sb hybridization and the large exchange splitting of the M atoms are responsible for the half-metallic property of some of these systems.

We study how the electronic structure of the bilayer graphene ͑BLG͒ is changed by electric field and strain from ab initio density-functional calculations using the linear muffin-tin orbital and the linear augmented plane wave methods. Both hexagonal and Bernal stacked structures are considered. We only consider interplanar strain where only the interlayer spacing is changed. The BLG is a zero-gap semiconductor like the isolated layer of graphene. We find that while strain alone does not produce a gap in the BLG, an electric field does so in the Bernal structure but not in the hexagonal structure. The topology of the bands leads to Dirac circles with linear dispersion in the case of the hexagonally stacked BLG due to the interpenetration of the Dirac cones, while for the Bernal stacking, the dispersion is quadratic. The size of the Dirac circle increases with the applied electric field, leading to an interesting way of controlling the Fermi surface. The external electric field is screened due to polarization charges between the layers, leading to a reduced size of the band gap and the Dirac circle. The screening is substantial in both cases and diverges for the Bernal structure for small fields as has been noted by earlier authors. As a biproduct of this work, we present the tight-binding parameters for the free-standing single layer graphene as obtained by fitting to the density-functional bands, both with and without the slope constraint for the Dirac cone and keeping the hopping integral up to four near neighbors.

We study the magnetic structure of the ͑LaMnO 3 ͒ 2n / ͑SrMnO 3 ͒ n superlattices from density-functional calculations. In agreement with the experiments, we find that the magnetism changes with the layer thickness n. The reason for the different magnetic structures is shown to be the varying potential barrier across the interface, which controls the leakage of the Mn-e g electrons from the LaMnO 3 side to the SrMnO 3 side. This in turn affects the interfacial magnetism via the carrier-mediated Zener double exchange. For the n = 1 superlattice, the Mn-e g electrons are more or less spread over the entire lattice so that the magnetic behavior is similar to the equivalent alloy compound La 2/3 Sr 1/3 MnO 3 . For larger n, the e g electron transfer occurs mostly between the two layers adjacent to the interface, thus leaving the magnetism unchanged and bulklike away from the interface region.

We study how strain affects orbital ordering and magnetism at the interface between SrMnO 3 and LaMnO 3 from density-functional calculations and interpret the basic results in terms of a three-site Mn-O-Mn model. Magnetic interaction between the Mn atoms is governed by a competition between the antiferromagnetic superexchange of the Mn t 2g core spins and the ferromagnetic double exchange of the itinerant e g electrons. While the core electrons are relatively unaffected by the strain, the orbital character of the itinerant electron is strongly affected, which in turn causes a large change in the strength of the ferromagnetic double exchange. The epitaxial strain produces the tetragonal distortion of the MnO 6 octahedron, splitting the Mn e g states into x 2 − y 2 and 3z 2 − 1 states, with the former being lower in energy, if the strain is tensile in the plane and opposite if the strain is compressive. For the case of the tensile strain, the resulting higher occupancy of the x 2 − y 2 orbital enhances the in-plane ferromagnetic double exchange owing to the larger electron hopping in the plane, causing at the same time a reduction in the out-of-plane double exchange. This reduction is large enough to be overcome by antiferromagnetic superexchange, which wins to produce a net antiferromagnetic interaction between the out-of-plane Mn atoms. For the case of the in-plane compressive strain, the reverse happens, viz., that the higher occupancy of the 3z 2 − 1 orbital results in the out-of-plane ferromagnetic interaction, while the in-plane magnetic interaction remains antiferromagnetic. Concrete density-functional results are presented for the ͑LaMnO 3 ͒ 1 / ͑SrMnO 3 ͒ 1 and ͑LaMnO 3 ͒ 1 / ͑SrMnO 3 ͒ 3 superlattices for various strain conditions.

Using density functional calculations we have investigated the local spin moment formation and lattice deformation in graphene when an isolated vacancy is created. We predict two competing equilibrium structures: a ground state planar configuration with a saturated local moment of 1.5 µB, and a metastable non-planar configuration with a vanishing magnetic moment, at a modest energy expense of 50 meV. Though non-planarity relieves the lattice of vacancy-induced strain, the planar state is energetically favored due to maximally localized defect states (vσ, vπ). In the planar configuration, charge transfer from itinerant (Dirac) states weakens the spin-polarization of vπ yielding a fractional moment, which is aligned parallel to the unpaired vσ electron through Hund's coupling. As a byproduct, the Dirac states (dπ) of the two sublattices undergo a minor spin-polarization and couple antiferromagnetically. In the non-planar configuration, the absence of orthogonal symmetry allows interaction between vσ and local dπ states, to form a hybridized vσ state. The non-orthogonality also destabilizes the Hund's coupling, and an antiparallel alignment between vσ and vπ lowers the energy. The gradual spin reversal of vπ with increasing non-planarity opens up the possibility of an intermediate structure with balanced vπ spin population. If such a structure is realized under external perturbations, diluted vacancy concentration may lead to vσ based spin-1/2 paramagnetism. Carrier doping, electron or hole, does not alter the structural stability. However, the doping proportionately changes the occupancy of vπ state and hence the net magnetic moment. arXiv:1605.03921v1 [cond-mat.mtrl-sci]

Density-functional electronic structure studies of a prototype interface between a paramagnetic metal and an antiferromagnetic (AFM) insulator (CaRuO(3)/CaMnO(3)) reveal the exponential leakage of the metallic electrons into the insulator side. The leaked electrons in turn control the magnetism at the interface via the ferromagnetic (FM) Anderson-Hasegawa double exchange, which competes with the AFM superexchange of the bulk CaMnO3. The competition produces a FM interfacial CaMnO3 layer (possibly canted); but beyond this layer, the electron penetration is insufficient to alter the bulk magnetism.

The unique structural characteristics make the 2D materials potential candidates for designing negative electrodes for rechargeable energy storage devices. Here, by employing density functional theory (DFT) calculations, we study the precise viability of using Si 2 BN, a graphene-like 2D material, as a high-capacity anode material for Mg-ion battery (MIB) application. The favorable Mg-adsorption sites with maximum possible coverage effect are explored in detail. It is found that the Si 2 BN sheet can be adsorbed to a configuration of Mg 8 Si 16 B 8 N 8 , which proposes a theoretical capacity of 647.896 mA h g −1 for divalent Mg 2+ -ion battery applications. The average open-circuit voltage of 0.6−0.7 V and intercalation migration energy barrier in the range of 0.08−0.35 eV make Si 2 BN one of the most promising anode materials for MIB applications. The porous Si 2 BN with high structural stability and metallic electronic structures along with the low Mg 2+ -ion migration barrier energies predict high electron and Mg-ion conductivity, ensuring fast charge/discharge cyclic performance. The above-mentioned findings validate that the Si 2 BN sheet can work as an excellent high-performance anode material for MIBs.