[en] The electronic structure of copper phthalocyanine (CuPc) monolayer was investigated by the first-principles all-electron full-potential linearized augmented plane wave (FLAPW) energy band method. The magnetic properties of the CuPc monolayer were investigated with spin-polarized calculation. It was found that the Cu atom has a magnetic moment of 0.56 μ_B, but it does not affect strongly the paramagnetic properties of the monolayer. The ground-state electronic structure of the CuPc monolayer found in spin-polarized calculation is indistinguishable from the paramagnetic case in the energy range from -10 to -1.5 eV and above 1.0 eV, with respect to the Fermi level (E_F), but taking into account the magnetic properties of the open-shell Cu atom results with the splitting of bands near E_F. The obtained total density of states and the calculated values of work function (4.66 eV) and ionization potential (5.23 eV) of the CuPc monolayer were found to be in a good agreement with the experimental data concerned CuPc thin films

[en] The surface electronic structures of superconducting MgB₂ were investigated using the all-electron full-potential linearized augmented plane-wave method. Hexagonal (0001) surfaces with both B terminated (B-Term) and Mg terminated (Mg-Term) were considered. Due to the nearly-free-electron nature of the Mg surface layer, the vacuum screening range of Mg-Term is shorter than that of B-Term, which shows the covalent bonding nature of the B surface layer. Considerably enhanced densities of states near the Fermi level are found at the surface layers especially for B-Term, which is expected to yield an enhanced superconductivity in the surface of thin film MgB₂ over that in bulk -- assuming no large changes in the electron-ion matrix elements and phonon frequency contributions. While this expectation is contrary to the weakened superconductivity observed in surface-oriented experiments, we attribute this discrepancy to extrinsic surface effects

[en] We have investigated the electronic structures and magnetism of an Fe nanowire along the [010] direction on a Cu(001) surface [Fe(W)/Cu(001)] by using the all-electron full-potential linearized augmented plane-wave method within the generalized gradient approximation. The Fe magnetic moment of the Fe(W)/Cu(001) is calculated to be 3.11 μ_B/atom, which is larger than that (2.82 μ_B/atom) of one monolayer of Fe on a Cu(001) surface [1Fe/Cu(001)], but smaller than that (3.39 μ_B/atom) of a free-standing Fe nanowire [free-Fe(W)]. We find that the reduced coordination number induces localizations of the Fe d-bands and exchange splitting enhancements of the Fe d-bands, which are responsible for the large magnetic moments of the Fe nanowires. The coordination numbers of the Fe atoms decrease from 8 for 1Fe/Cu(001), to 4 for Fe(W)/Cu(001), and to 2 for free-Fe(W). The calculated spin-polarized layer-projected density of states confirm the localizations of the Fe d-bands and the exchange splitting enhancements of the Fe d-bands.

[en] We investigated the multilayer relaxations of Fe(601) surface and their effects on the magnetism and the electronic structures by using the all-electron total-energy full-potential linearized augmented plane wave (FLAPW) method within the generalized gradient approximation (GGA) for the exchange-correlation potential. We found, from the calculated bond lengths of each atom, that the atomic relaxations tend to smooth the edges with a 100 % contraction of the interlayer distance between the edge atoms. The calculated local magnetic moments depend mostly on the coordination numbers rather than on the interatomic bond lengths. The magnetic moment (M) dependency on the dimensionless geometrical factor x, which is defined by the ratio between the coordination number and the average bond length of a specific atom, is quantitatively analyzed to propose an empirical rule of M / x − , where is geometry-dependent exponent. From the calculated density of states, we found that the surface localization effects determine the magnetic moments of the surface atoms, including the edge atoms. However, the geometrical complications of the edge atoms provide the reason for the local magnetic moments of the edge atoms being smaller than those of the terrace atoms.

[en] External pressure driven phase transitions of FeSe are predicted using ab initio calculations. The calculations reveal that α-FeSe makes transitions to NiAs-type, MnP-type, and CsCl-type FeSe. Transitions from NiAs-type to MnP-type and CsCl-type FeSe are also predicted. MnP-type FeSe is also found to be able to transform to CsCl-type FeSe, which is easier from α-FeSe than the transition to MnP-type FeSe, but comparable to the transition from NiAs-type FeSe. The calculated electronic structures show that all phases of FeSe are metallic, but the ionic interaction between Fe-Se bonds becomes stronger and the covalent interaction becomes weaker when the structural phase transition occurs from α-FeSe to the other phases of FeSe. The experimentally observed decrease in T_c of superconducting α-FeSe at high pressure may be due to a structural/magnetic instability, which exists at high pressure. The results suggest an increase of the T_c of α-FeSe if such phase transitions are frustrated by suitable methods. (paper)

[en] Strong perpendicular magnetocrystalline anisotropy (MCA) and low saturation magnetization are found in DO₂₂ Mn₃Ga using the full-potential linearized augmented plane wave (FLAPW) method. The ferrimagnetism in the bulk is well preserved in the surfaces of Mn₃Ga for two possible terminations, where the perpendicular MCA in the (001) direction is greatly enhanced over the bulk, consistent with experiments. Furthermore, the robustness of MCA with respect to lattice strain and a good lattice match with popular substrates suggest that Mn₃Ga can be a good candidate for strain-resistance spintronics applications.

[en] There is now a large number of sophisticated steels which rely on silicon as an alloying addition with the purpose of avoiding the precipitation of cementite. However, there is also evidence that the silicon can enhance the formation of ε-carbide; the mechanism of this effect is not understood and the absence of appropriate thermodynamic data makes it impossible to conduct calculations. We report here some ab initio calculations which throw light on both of these issues and suggest novel experiments.