Maximally localized Wannier functions within the FLAPW formalism

Electronic tunneling through ferroelectric insulators is considered to be a key ingredient of future oxide electronics. We investigate the role of the electronic band structure of the decaying electronic states in the band gap by first discussing the expected behavior of tunneling in the effective mass model. We demonstrate that, even for the simple prototype ferroelectric oxides in the perovskite structures PbTiO 3 and BaTiO 3 , the basic assumption of the effective mass model is not appropriate, and that the correct interpretation of tunneling in these materials requires a material-specific description of the evanescent states as provided by the complex band structure.

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“…The very same structure has been presented in Ref. 27 and its ferroelectric polarization has been calculated to be 49 μC/cm 2 .…”

Section: Complex Band Structure Of Ferroelectricssupporting

confidence: 49%

Influence of the electronic structure on tunneling through ferroelectric insulators: Application to BaTiO3and PbTiO33

Wortmann

Blügel

2011

Phys. Rev. B

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“…50 The Wannier functions technique was used on top of self-consistent first-principles calculations to derive an accurate tight-binding Hamiltonian of the system. [51][52][53] Both Bi(111) and Sb(111) bilayers considered in this work have buckled honeycomb lattice structure. The relaxed bulk in-plane lattice constant and the distance between the two layers for Sb(111) constitute 4.30 and 1.55Å, respectively, while for Bi(111) bilayer the corresponding values are 4.52 and 1.67Å.…”

Section: Topological States Of Bi and Sb Bilayersmentioning

confidence: 99%

Engineering quantum anomalous Hall phases with orbital and spin degrees of freedom

et al. 2013

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Combining tight-binding models and first-principles calculations, we investigate the quantum anomalous Hall (QAH) effect induced by intrinsic spin-orbit coupling (SOC) in buckled honeycomb lattice with sp orbitals in an external exchange field. Detailed analysis reveals that nontrivial topological properties can arise utilizing not only spin but also orbital degrees of freedom in the strong SOC limit, when the bands acquire nonzero Chern numbers upon undergoing the so-called orbital purification. As a prototype of a buckled honeycomb lattice with strong SOC we choose the Bi(111) bilayer, analyzing its topological properties in detail. In particular, we show the emergence of several QAH phases upon spin exchange of the Chern numbers as a function of SOC strength and magnitude of the exchange field. Interestingly, we observe that in one of such phases, namely, in the quantum spin Chern insulator phase, the quantized charge and spin Hall conductivities coexist. We consider the possibility of tuning the SOC strength in the Bi bilayer via alloying with isoelectronic Sb, and speculate that exotic properties could be expected in such an alloyed system owing to the competition of the topological properties of its constituents. Finally, we demonstrate that 3d dopants can be used to induce a sizable exchange field in the Bi(111) bilayer, resulting in nontrivial Chern insulator properties.

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“…III C. However, these wave functions are, in general, unknown. Therefore, we employ the Wannierinterpolation technique [47][48][49] as realized in the WANNIER90 code 50 to interpolate the band energies between the ones of the k mesh. As an example Fig.…”

Section: Calculationsmentioning

confidence: 99%

Hybrid functionals within the all-electron FLAPW method: Implementation and applications of PBE0

2010

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We present an efficient implementation of the Perdew-Burke-Ernzerhof hybrid functional PBE0 within the full-potential linearized augmented-plane-wave ͑FLAPW͒ method. The Hartree-Fock exchange term, which is a central ingredient of hybrid functionals, gives rise to a computationally expensive nonlocal potential in the one-particle Schrödinger equation. The matrix elements of this exchange potential are calculated with the help of an auxiliary basis that is constructed from products of FLAPW basis functions. By representing the Coulomb interaction in this basis the nonlocal exchange term becomes a Brillouin-zone sum over vector-matrixvector products. The Coulomb matrix is calculated only once at the beginning of a self-consistent-field cycle. We show that it can be made sparse by a suitable unitary transformation of the auxiliary basis, which accelerates the computation of the vector-matrix-vector products considerably. Additionally, we exploit spatial and time-reversal symmetry to identify the nonvanishing exchange matrix elements in advance and to restrict the k summations for the nonlocal potential to an irreducible set of k points. Favorable convergence of the selfconsistent-field cycle is achieved by a nested density-only and density-matrix iteration scheme. We discuss the convergence with respect to the parameters of our numerical scheme and show results for a variety of semiconductors and insulators, including the oxides ZnO, EuO, Al 2 O 3 , and SrTiO 3 , where the PBE0 hybrid functional improves the band gaps and the description of localized states in comparison with the PBE functional. Furthermore, we find that in contrast to conventional local exchange-correlation functionals ferromagnetic EuO is correctly predicted to be a semiconductor.

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Maximally localized Wannier functions within the FLAPW formalism

Cited by 159 publications

References 40 publications

Influence of the electronic structure on tunneling through ferroelectric insulators: Application to BaTiO3and PbTiO33

Influence of the electronic structure on tunneling through ferroelectric insulators: Application to BaTiO3and PbTiO33

Engineering quantum anomalous Hall phases with orbital and spin degrees of freedom

Hybrid functionals within the all-electron FLAPW method: Implementation and applications of PBE0

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