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Oct 28 2014
Authors: | Sylvia Wenmackers, Danny E. P. Vanpoucke, and Igor Douven |
Journal: | Front. Psychol. 5, 581 (2014) |
doi: | 10.3389/fpsyg.2014.00581 |
IF(2014): | 2.560 |
export: | bibtex |
pdf: | <Front.Psychol.> (open Access) |
Both in philosophy and in psychology, human rationality has traditionally been studied from an ‘individualistic’ perspective. Recently, social epistemologists have drawn attention to the fact that epistemic interactions among agents also give rise to important questions concerning rationality. In previous work, we have used a formal model to assess the risk that a particular type of social-epistemic interactions lead agents with initially consistent belief states into inconsistent belief states. Here, we continue this work by investigating the dynamics to which these interactions may give rise in the population as a whole.
Oct 28 2014
Authors: | Danny E. P. Vanpoucke |
Journal: | J. Comput. Chem. 34(5), i-ii (2013) |
doi: | 10.1002/jcc.23239 |
IF(2013): | 3.601 |
export: | bibtex |
pdf: | <J.Comput.Chem.> |
The image shows an isosurface of Hirshfeld-I “atoms in molecules” for Ti-doped CeO2, taken at an electron density of 0.03e/Å3, as presented by Danny E. P. Vanpoucke, Patrick Bultinck, and Isabel Van Driessche on page 405. The cubic Ce0.75Ti0.25O2 unit cell is shown along the 111 direction. The different atoms are still clearly distinguishable at this iso-surface level, and show the Ti atom in the corners to be much smaller than the Ce atoms on the sides. In this issue, this implementation of the Hirshfeld- I method for solids is published back to back with a Comment from Thomas A. Manz and the authors’ Reply.
Oct 28 2014
Authors: | Danny E. P. Vanpoucke, Isabel Van Driessche, and Patrick Bultinck |
Journal: | J. Comput. Chem. 34(5), 422-427 (2013) |
doi: | 10.1002/jcc.23193 |
IF(2013): | 3.601 |
export: | bibtex |
pdf: | <J.Comput.Chem.> <arXiv> |
Graphical Abstract:The issues raised in the preceding comment are addressed. It is shown why Hirshfeld-I is, from a theoretical point of view, a good method for defining AIM and obtaining charges. Charges for a set of ionic systems are calculated using our presented method and shown to be chemically feasable. Comparison of pseudo-density to all-electron based results shows the pseudo-densities to be sufficient to obtain all-electron quality results. Timing results for systems containing hundreds of atoms. |
The issues raised in the comment by Manz are addressed through the presentation of calculated atomic charges for NaF, NaCl, MgO, SrTiO3, and La2Ce2O7, using our previously presented method for calculating Hirshfeld-I charges in solids (Vanpoucke et al., J. Comput. Chem. doi: 10.1002/jcc.23088). It is shown that the use of pseudovalence charges is sufficient to retrieve the full all-electron Hirshfeld-I charges to good accuracy. Furthermore, we present timing results of different systems, containing up to over 200 atoms, underlining the relatively low cost for large systems. A number of theoretical issues are formulated, pointing out mainly that care must be taken when deriving new atoms in molecules methods based on “expectations” for atomic charges.
Oct 28 2014
Authors: | Danny E. P. Vanpoucke, Patrick Bultinck, and Isabel Van Driessche, |
Journal: | J. Comput. Chem. 34(5), 405-417 (2013) |
doi: | 10.1002/jcc.23088 |
IF(2013): | 3.601 |
export: | bibtex |
pdf: | <J.Comput.Chem.> <arXiv> |
Graphical Abstract: The Hirshfeld-I method is extended to solids, allowing for the partitioning of a solid density into constituent atoms. The use of precalculated density grids makes the implementation code independent, and the use of pseudo-potential based electron density distributions is shown to give qualitatively the same results as all electron densities. Results for some simple solids/periodic systems like cerium oxide and graphene are presented. |
In this work, a method is described to extend the iterative Hirshfeld-I method, generally used for molecules, to periodic systems. The implementation makes use of precalculated pseudopotential-based electron density distributions, and it is shown that high-quality results are obtained for both molecules and solids, such as ceria, diamond, and graphite. The use of grids containing (precalculated) electron densities makes the implementation independent of the solid state or quantum chemical code used for studying the system. The extension described here allows for easy calculation of atomic charges and charge transfer in periodic and bulk systems. The conceptual issue of obtaining reference densities for anions is discussed, and the delocalization problem for anionic reference densities originating from the use of a plane wave basis set is identified and handled.
Oct 28 2014
Authors: | Sylvia Wenmackers, Danny E. P. Vanpoucke, and Igor Douven |
Journal: | Eur. Phys. J. B 85, 44 (2012) |
doi: | 10.1140/epjb/e2011-20617-8 |
IF(2012): | 1.282 |
export: | bibtex |
pdf: | <Eur.Phys.J.B> |
We present a model for studying communities of epistemically interacting agents who update their belief states by averaging (in a specified way) the belief states of other agents in the community. The agents in our model have a rich belief state, involving multiple independent issues which are interrelated in such a way that they form a theory of the world. Our main goal is to calculate the probability for an agent to end up in an inconsistent belief state due to updating (in the given way). To that end, an analytical expression is given and evaluated numerically, both exactly and using statistical sampling. It is shown that, under the assumptions of our model, an agent always has a probability of less than 2% of ending up in an inconsistent belief state. Moreover, this probability can be made arbitrarily small by increasing the number of independent issues the agents have to judge or by increasing the group size. A real-world situation to which this model applies is a group of experts participating in a Delphi-study.
Oct 28 2014
Authors: | Danny E. P. Vanpoucke, Stefaan Cottenier, Veronique Van Speybroeck, Patrick Bultinck, and Isabel Van Driessche, |
Journal: | Appl. Surf. Sci. 260, 32-35 (2012) |
doi: | 10.1016/j.apsusc.2012.01.032 |
IF(2012): | 2.112 |
export: | bibtex |
pdf: | <Appl.Surf.Sci.> <arXiv> |
The appearance of microcracks in cerium oxide (CeO2) buffer layers, as used in buffer layer architectures for coated superconductors, indicates the presence of stress between this buffer layer and the substrate. This stress can originate from the differences in thermal expansion or differences in lattice parameters between the CeO2 buffer layer and the substrate. In this article, we study, by means of ab initio density functional theory calculations, the influence of group IV doping elements on the lattice parameter and bulk modulus of CeO2. Vegard’s law behavior is found for the lattice parameter in systems without oxygen vacancies, and the Shannon crystal radii for the doping elements are retrieved from the lattice expansions. We show that the lattice parameter of the doped CeO2 can be matched to that of the La2Zr2O7 coated NiW substrate substrate for dopant concentrations of about 5%, and that bulk modulus matching is either not possible or would require extreme doping concentrations.
Oct 28 2014
Authors: | Sylvia Wenmackers and Danny E. P. Vanpoucke |
Journal: | Statistica Neerlandica 66, 339-355 (2012) |
doi: | 10.1111/j.1467-9574.2011.00519.x |
IF(2012): | 0.585 |
export: | bibtex |
pdf: | <Stat.Neer.> <arXiv> |
We discuss two research projects in material science in which the results cannot be stated with an estimation of the error: a spectroscopic ellipsometry study aimed at determining the orientation of DNA molecules on diamond and a scanning tunneling microscopy study of platinum-induced nanowires on germanium. To investigate the reliability of the results, we apply ideas from the philosophy of models in science. Even if the studies had reported an error value, the trustworthiness of the result would not depend on that value alone.
Oct 28 2014
Authors: | Vyshnavi Narayanan, Petra Lommens, Klaartje De Buysser, Danny E.P. Vanpoucke, Ruben Huehne, Leopoldo Molina, Gustaaf Van Tendeloo , Pascal Van Der Voort, Isabel Van Driessche |
Journal: | J. Mater. Chem. 22, 8476-8483 (2012) |
doi: | 10.1039/C2JM15752G |
IF(2012): | 6.101 |
export: | bibtex |
pdf: | <J.Mater.Chem.> |
Lanthanum–cerium oxide (LCO) films were deposited on Ni-5%W substrates by chemical solution deposition (CSD) from water-based precursors. LCO films containing different ratios of lanthanum and cerium ions (from CeO2 to La2Ce2O7) were prepared. The composition of the layers was optimized towards the formation of LCO buffer layers, lattice-matched with the superconducting YBa2Cu3Oy layer, useful for the development of coated conductors. Single, crack-free LCO layers with a thickness of up to 140 nm could be obtained in a single deposition step. The crystallinity and microstructure of these lattice-matched LCO layers were studied by X-ray diffraction techniques, RHEED and SEM. We find that only layers with thickness below 100 nm show a crystalline top surface although both thick and thin layers show good biaxial texture in XRD. On the most promising layers, AFM and (S)TEM were performed to further evaluate their morphology. The overall surface roughness varies between 3.9 and 7.5 nm, while the layers appear much more dense than the frequently used La2Zr2O7 (LZO) systems, showing much smaller nanovoids (1–2 nm) than the latter system. Their effective buffer layer action was studied using XPS. The thin LCO layers supported the growth of superconducting YBCO deposited using PLD methods.
Oct 28 2014
Authors: | Danny E.P. Vanpoucke |
Ph.D. Thesis | at Ghent University, Belgium |
date: | October 5th, 2012 |
Promoters | Prof. Dr. Isabel Van Driessche and Prof. Dr. Patrick Bultinck |
#pages | 218 |
export: | bibtex |
pdf: | <PhD.Thesis> |
research page with more information |
High temperature ceramic superconductors can be grown in layered structures on metallic wires to provide the mechanical flexibility required for industrial applications. To prevent the metal atoms of diffusing into the superconductor—destroying its superconductivity—buffer layers are grown between the metal substrate and the superconductor. Recently, cerium oxide has been used as such a buffer layer. However, the layer thickness of these buffer layers is limited by the formation of cracks during deposition. This behaviour has been linked to internal stress due to lattice mismatch and different thermal expansion coefficients of the substrate and the buffer layer. A simple way to reduce these mismatches is through metal doping.
In this work, we study the influence of dopants on the properties of cerium oxide through the use of ab initio calculations. Trends in the stability, lattice parameter, bulk modulus and thermal expansion coefficient of cerium oxide doped with different dopants are investigated. In addition, the influence of charge compensating oxygen vacancies is studied, and their role in the stability of heavily La-doped cerium oxide (La2Ce2O7) is presented. The use of dopants with different valences also leads to a modification of the charge distribution around the dopant sites. A way to have a more quantitative estimate of the charge transfer induced by dopants is via the introduction of the chemical concept of ‘atoms in a molecule’ into solids. This can be considered a first step in the direction of answering the experimental question: What is the charge of a given atom in a certain compound? In this work we present an implementation of this Hirshfeld method for solids, and calculate the atomic charges in doped cerium oxides.