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Castleton, Christopher
Publications (2 of 2) Show all publications
Castleton, C., Nokbin, S. & Hermansson, K. (2007). Correlations between magnetic properties and bond formation in Rh-MgO(0 0 1). Surface Science, 601(5), 1218-1230
Open this publication in new window or tab >>Correlations between magnetic properties and bond formation in Rh-MgO(0 0 1)
2007 (English)In: Surface Science, ISSN 0039-6028, E-ISSN 1879-2758, Vol. 601, no 5, p. 1218-1230Article in journal (Refereed) Published
Abstract [en]

We present the results of first principles calculations for the magnetism of Rh adlayers on MgO(0 0 1), at three different adsorption sites and three different coverages, corresponding to 1, 1/2 and 1/8 monolayers. Finite magnetization is found in all cases except that of one Rh monolayer above the oxygen site, which is also the most stable. We examine how the magnetization changes as a function of the Rh-surface distance and relate this to changes in the real-space charge density and in the density of states (DOS) as the Rh adlayer interacts with the surface. We find that increasing either the Rh-Rh interaction strength or the Rh-surface interaction strength leads to reduced magnetization, while increasing the former drives a crossover from localized (atomic) to itinerant magnetism. Neither the magnetic transition itself, nor the localized-to-itinerant magnetism crossover, is found to be directly related to the formation of Rh-surface bonds. From a practical point of view, we predict that magnetism in the Rh-MgO(0 0 1) system is most likely to be found experimentally at reduced coverages and at low temperatures. © 2006 Elsevier B.V. All rights reserved.

Keywords
Adatoms, Adhesion, Density functional calculations, Electron density, Excitation spectra calculations, Magnesium oxides, Magnetic films, Magnetic phenomena (cyclotron resonance, phase transitions, etc.), Rhodium
National Category
Engineering and Technology
Identifiers
urn:nbn:se:liu:diva-49963 (URN)10.1016/j.susc.2006.12.061 (DOI)
Available from: 2009-10-11 Created: 2009-10-11 Last updated: 2017-12-12
Castleton, C., Kullgren, J. & Hermansson, K. (2007). Tuning LDA+U for electron localization and structure at oxygen vacancies in ceria. Journal of Chemical Physics, 127(24)
Open this publication in new window or tab >>Tuning LDA+U for electron localization and structure at oxygen vacancies in ceria
2007 (English)In: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 127, no 24Article in journal (Refereed) Published
Abstract [en]

We examine the real space structure and the electronic structure (particularly Ce4f electron localization) of oxygen vacancies in Ce O2 (ceria) as a function of U in density functional theory studies with the rotationally invariant forms of the LDA+U and GGA+U functionals. The four nearest neighbor Ce ions always relax outwards, with those not carrying localized Ce4f charge moving furthest. Several quantification schemes show that the charge starts to become localized at U˜3 eV and that the degree of localization reaches a maximum at ~6 eV for LDA+U or at ~5.5 eV for GGA+U. For higher U it decreases rapidly as charge is transferred onto second neighbor O ions and beyond. The localization is never into atomic corelike states, at maximum localization about 80-90% of the Ce4f charge is located on the two nearest neighboring Ce ions. However, if we look at the total atomic charge we find that the two ions only make a net gain of (0.2-0.4) e each, so localization is actually very incomplete, with localization of Ce4f electrons coming at the expense of moving other electrons off the Ce ions. We have also revisited some properties of defect-free ceria and find that with LDA+U the crystal structure is actually best described with U=3-4 eV, while the experimental band structure is obtained with U=7-8 eV. (For GGA+U the lattice parameters worsen for U>0 eV, but the band structure is similar to LDA+U.) The best overall choice is U˜6 eV with LDA+U and ˜5.5 eV for GGA+U, since the localization is most important, but a consistent choice for both Ce O2 and Ce2 O3, with and without vacancies, is hard to find. © 2007 American Institute of Physics.

National Category
Engineering and Technology
Identifiers
urn:nbn:se:liu:diva-47643 (URN)10.1063/1.2800015 (DOI)
Available from: 2009-10-11 Created: 2009-10-11 Last updated: 2017-12-13
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