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Transition-metal containing metal phthalocyanine (MPc) molecules are representative molecular magnets and their adsorption on two-dimensional metallic surfaces has been extensively studied. In/Si(111)-4×1 is a prototypical quasi-one-dimensional metallic surface made up of alternating In nanowires and Si Seiwatz chains. Here, we investigated the adsorption of MPc (M = Mn, Fe, Co) on In/Si(111)-4×1 using density functional theory calculations. We found that there are three locally stable adsorption sites of MPc, two on In nanowires and one on Seiwatz chains. Also, the stable orientation of MPc is different depending on adsorption sites. Among three MPc’s, MnPc are found to carry a finite magnetic moment of 1.6 ~ 2.1 μBin its three almost-degenerate adsorption structures. The interaction between MPc molecules and the In/Si(111)-4×1 surface turns out to occur via the charge transfer, and the charge transfer channel varies for different adsorption sites: Transition-metal 3dz2 and two N 2pzorbitals on In nanowires vs.four N 2pzorbitals on Seiwatz chains.

The electronic structures and the thermoelectric (TE) properties of the ternary chalcogenide PbBi4Te7are investigated by using first-principles calculations within the density functional theory and the solutions of semi-classical Boltzmann equation. Employing the screened-exchange local density approximation, we found that PbBi4Te7to be a narrow-gap semiconductor with an indirect band gap of 0.11 eV. The combination of light and heavy valence bands near the band edge gives rise to large Seebeck coefficients, S, for p-type doping, which is found to be improved by 11% from that of Bi2Te3at room temperature (RT). Moreover, in contrast to conventional Bi2Te3where the value of Sdecreases rapidly with temperatures higher than RT, the values of Sincreases with temperature reaching up to 350 μVK−1at 500 K indicating that PbBi4Te7is a promising TE material with operating temperatures above RT. Our result also reveals that the intrinsic layered structure results in a prominent anisotropy in the TE coefficients, implying that the TE performance can be optimized by using the transport direction, as well as the type and the level of doping.

The FePt3alloy is one of the most investigated materials for high density storage applications due to its rich variety of magnetic structures which transform sensitively depending on change in its local structure. Here, we present the ab-initiototal energy and electronic structure calculations within the framework of density functional theory for an FePt3film of 0.5 nm in thickness on a Pt (110) surface. The results show that a missing-row surface reconstruction along the $$[1\overline 1 0]$$direction is energetically more stable over the unreconstructed clean surface, which is attributed to the energy gain by the spill out of p-electron charge to the large facet area from Pt atoms at the second and third atomic layers. The missing-row reconstruction is found to enhance the stability of the ferromagnetic phase over the antiferromagnetic bulk ground-state phase and to induce possible concurrence of a meta-stable atomic structure with an in-plane anti-phase boundary along the orientation of missing-row in addition to the conventional L12surface, implying the observation of various magnetic phases.

We report our ab - initiocalculational results for the electronic structures and the magnetooptical (MO) properties of the ferromagnetic Co2MnXfull Heusler alloys where X= Ge, Sn and Pb. Employing the +U corrections for the 3dbands of transition-metal atoms in addition to the conventional local density approximation (LDA), we investigate the correlation effect on the MO spectra in a polar geometry and the detailed electronic structures. Results show that the correlation effect results in a blue-shift of the peak positions and a large enhancement of the MO spectra up to double in magnitude compared to the LDA results. We find that our results can be attributed to the increased t2g− egsplitting of the spin-minority d-bands of both Co and Mn atoms, which indicates a suppression of the diagonal elements of the optical conductivity in the energy region of 1–2 eV where the interband transitions are forbidden.

We performed an ab-initioelectronic structure calculation for the bismuth selenide compound with oxygen substitution by using the all-electron full-potential linearized augmented plane-wave (FLAPW) method. The spin-orbit coupling in the second variational scheme and the screenedexchange local density approximation (sX-LDA) were adapted, and a large enhancement of the indirect band gap from 0.13 to 0.78 eV over the conventional LDA result was found. Exploiting the FLAPW wave-functions, we employed Boltzmann’s equation in a constant relaxation-time approach to estimate the thermoelectric (TE) transport properties, including the Seebeck coefficient, the electrical conductivity and the power factor. The temperature and the carrier-concentration dependences of the TE properties were investigated in detail to find the effect of oxygen substitution on and to search for the optimal doping and temperature range for better thermoelectric performance.

Abstract: We report the ab-initio calculational results for the half-metallicity of the Co2FeSi full Heusler alloy in (001) surfaces. Employing the +U corrections, in addition to the local density approximation (LDA) and generalized gradient approximation (GGA), we investigate the effects of surface and correlation interactions on the half-metallicity and the magnetic properties. The (001) surfaces are calculated to be metallic by both the LDA and the GGA due to the surface states the develop at the Fermi energy (E F ). Upon +U correction, the surface states are pushed down below E F for the Co-terminated surface, which recovers the half-metallicity with a reduced band gap of 0.40 eV. In contrast, the FeSi-terminated surface is predicted to be metallic because the surface states remain at the Fermi level in spite of an enhanced t 2g −e g band splitting caused by the correlation effect.