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Subject: Density functional theory × WGL Institute: IFWD ×

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Now showing 1 - 3 of 3
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    Visualization of localized perturbations on a (001) surface of the ferromagnetic semimetal EuB6
    (College Park, MD : American Physical Society, 2020) Rößler, S.; Jiao, L.; Seiro, S.; Rosa, P.F.S.; Fisk, Z.; Rößler, U.K.; Wirth, S.
    We performed scanning tunneling microscopy (STM) and spectroscopy on a (001) surface of the ferromagnetic semimetal EuB6. Large-amplitude oscillations emanating from the elastic scattering of electrons by the surface impurities are observed in topography and in differential conductance maps. Fourier transform of the conductance maps embracing these regions indicate a holelike dispersion centered around the Γ point of the two-dimensional Brillouin zone. Using density functional theory slab calculations, we identify a spin-split surface state, which stems from the dangling pz orbitals of the apical boron atom. Hybridization with bulk electronic states leads to a resonance enhancement in certain regions around the Γ point, contributing to the remarkably strong real-space response around static point defects, which are observed in STM measurements.
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    Accuracy and Precision in Electronic Structure Computation: Wien2k and FPLO
    (Basel : MDPI, 2022) Richter, Manuel; Kim, Seo-Jin; Koepernik, Klaus; Rosner, Helge; Möbius, Arnulf
    Electronic structure calculations in the framework of density functional theory are based on complex numerical codes which are used in a multitude of applications. Frequently, existing experimental information is used as a gauge for the reliability of such codes. However, their results depend both on the chosen exchange-correlation energy functional and on the specific numerical implementation of the Kohn-Sham equations. The only way to disentangle these two items is a direct comparison of two or more electronic structure codes. Here, we address the achievable numerical accuracy and numerical precision in the total energy computation of the two all-electron density-functional codes Wien2k and FPLO. Both codes are based on almost independent numerical implementations and largely differ in the representation of the Bloch wave function. Thus, it is a highly encouraging result that the total energy data obtained with both codes agree within less than 10−6. We here relate the term numerical accuracy to the value of the total energy E, while the term numerical precision is related to the numerical noise of E as observed in total energy derivatives. We find that Wien2k achieves a slightly higher accuracy than FPLO at the price of a larger numerical effort. Further, we demonstrate that the FPLO code shows somewhat higher precision, i.e., less numerical noise in E than Wien2k, which is useful for the evaluation of physical properties based on derivatives of E.
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    Structural stability, electronic, optical, and thermoelectric properties of layered perovskite Bi2LaO4I
    (London : RSC Publishing, 2022) Joshi, Radha K.; Bhandari, Shalika R.; Ghimire, Madhav Prasad
    Layered perovskites are an interesting class of materials due to their possible applications in microelectronics and optoelectronics. Here, by means of density functional theory calculations, we investigated the structural, elastic, electronic, optical, and thermoelectric properties of the layered perovskite Bi2LaO4I within the parametrization of the standard generalized gradient approximation (GGA). The transport coefficients were evaluated by adopting Boltzmann semi-classical theory and a collision time approach. The calculated elastic constants were found to satisfy the Born criteria, indicating that Bi2LaO4I is mechanically stable. Taking into account spin-orbit coupling (SOC), the material was found to be a non-magnetic insulator, with an energy bandgap of 0.82 eV (within GGA+SOC), and 1.85 eV (within GGA+mBJ+SOC). The optical-property calculations showed this material to be optically active in the visible and ultraviolet regions, and that it may be a candidate for use in optoelectronic devices. Furthermore, this material is predicted to be a potential candidate for use in thermoelectric devices due to its large value of power factor, ranging from 2811 to 7326 μW m−1 K−2, corresponding to a temperature range of 300 K to 800 K.