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Suche nach „[David] [Scholz]“ hat 5 Publikationen gefunden
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    NachhaltigAngewandte Naturwissenschaften und Wirtschaftsingenieurwesen

    Zeitschriftenartikel

    Thomas Stirner, David Scholz, J. Sun

    Convergence of surface energy calculations for various methods: (001), (012), (100) hematite and the applicability of the standard approach

    Journal of Physics: Condensed Matter, vol. 32, no. 18

    2020

    DOI: 10.1088/1361-648X/ab6f88

    Abstract anzeigen

    Three different methods for the calculation of the surface energy, namely the standard approach, the Boettger relation and the linear-fit method, are applied to the (0 0 1), (0 1 2) and (1 0 0) hematite surfaces. The standard approach was previously shown to suffer from a divergence problem, and the Boettger relation was shown to exhibit quantum size effects. While the linear-fit method, in general, leads to a good convergence behavior of the surface energy, the questions arise whether the relative order of the calculated surface energies depends on the chosen calculation method, and whether there is any merit at all in employing the standard approach. The present work investigates these questions with hematite as a benchmark material system. The simulations show that, for the surface facets and slab thicknesses studied here, the relative order of the surface energies is unaffected by the chosen calculation method. A regime is found where the three methods are in reasonably good agreement with respect to the obtained surface energies. Finally, a procedure is put forward to extract meaningful surface energy values from the standard approach.

    NachhaltigAngewandte Naturwissenschaften und Wirtschaftsingenieurwesen

    Zeitschriftenartikel

    David Scholz, Thomas Stirner

    Convergence of surface energy calculations for various methods: (0 0 1) hematite as benchmark

    Journal of Physics: Condensed Matter, vol. 31, no. 19

    2019

    DOI: 10.1088/1361-648X/ab069d

    Abstract anzeigen

    Different methods for calculating the surface energy from ab initio simulations are applied to the relaxed (0 0 1) surface of the metal oxide hematite (α-Fe2O3). The simulations are carried out with a rather moderate k-point grid with shrinking factors of (6 6 6) for all bulk and (6 6) for all slab simulations. Very good convergence is obtained if a linear fit of the slab energies with respect to the number of layers in the slab is performed. In comparison to the other methods employed, this procedure is ultimately the most accurate and reliable method for extracting convergent surface energies from (0 0 1) hematite slabs. Additionally, we propose a way to determine the least possible starting point for calculating the surface energy by the linear-fit method. Furthermore, we find the Boettger method to perform nearly equally well, if the bulk energy is extracted from the energy difference per layer between the slabs with 12 and 18 layers thickness. Both methods give a surface energy of 2.43 J m-2 with a deviation of less than ±0.005 J m-2. The standard approach, which uses a separate bulk simulation, instead shows a significant linear divergence with increasing number of layers in the slab. We also carried out bulk simulations with a surface-oriented bulk unit cell, but found it in our case not to improve the convergence of the standard approach.

    NachhaltigAngewandte Naturwissenschaften und Wirtschaftsingenieurwesen

    Zeitschriftenartikel

    Thomas Stirner, David Scholz, J. Sun

    Ab initio simulation of structure and surface energy of low-index surfaces of stoichiometric alpha-Fe2O3

    Surface Science, vol. 671, no. May, pp. 11-16

    2018

    DOI: 10.1016/j.susc.2018.01.010

    Abstract anzeigen

    The structure and surface energy of a series of low-index surfaces of stoichiometric α-Fe2O3 (hematite) are investigated using the periodic Hartree–Fock approach with an a posteriori correction of the correlation energy. The simulations show that, amongst the modeled facets, (012) and (0001) are the most stable surfaces of hematite, which is consistent with the fact that the latter are the dominant growth faces exposed on natural α-Fe2O3. The Fe-terminated (0001) surface is shown to exhibit a large relaxation of the surface atoms. It is argued that this arises mainly due to the fact that the surface cations are located opposite empty cation sites in the filled-filled-unfilled cation sequence along the c-axis. In contrast, the (012) plane cuts the crystal through a plane of empty cation sites, thus giving rise to relatively small relaxations and surface energies. The small relaxations and concomitant exposure of five-coordinate cation sites may be important for the catalytic activity of hematite. The simulations also show that the relative stability of the investigated surfaces changes after a full lattice relaxation with the (0001) and (116) facets relaxing disproportionately large. Wherever possible, the simulations are compared with previous simulation data and experimental results. A Wulff–Gibbs construction is also presented.

    NachhaltigMaschinenbau und Mechatronik

    Zeitschriftenartikel

    Thomas Stirner, David Scholz, J. Sun

    Hartree-Fock simulation of the (0 0 0 1) surface of hematite with a posteriori calculation of the correlation energy

    Computational Materials Science, vol. 137, no. September, pp. 340-345

    2017

    DOI: 10.1016/j.commatsci.2017.06.011

    Abstract anzeigen

    The results of Hartree-Fock simulations of the (0 0 0 1) surface of hematite including an a posteriori calculation of the correlation energy are presented. Structural as well as electronic and magnetic properties of the surface atoms are considered. Infrared and Raman bands of the hematite slab are also presented. The calculated surface relaxation is shown to be in good agreement with experimental data originating from a recent LEED analysis. The iron-oxygen bond at the single-iron-terminated surface is shown to be less ionic than in the bulk. Also, the magnetic dipole moment of the surface iron atom is smaller than in the bulk. Finally, the surface energy of the (0 0 0 1) facet is presented for hematite, and for comparison also for α-alumina and α-chromia for various hybrid functionals. Here it is shown that the effects of electron correlation play an important role for hematite and chromia due to their localized 3d electrons.

    NachhaltigAngewandte Naturwissenschaften und Wirtschaftsingenieurwesen

    Vortrag

    David Scholz, Thomas Stirner

    Hartree-Fock simulation of hematite surfaces with a posteriori calculation of correlation energy

    Preisträgervortrag zur Verleihung des Georg-Simon-Ohm-Preises der Deutschen Physikalischen Gesellschaft an David Scholz

    DPG-Frühjahrstagung, Dresden (abgesagt wegen Covid-19, gehalten an THD), Dresden