527 research outputs found
The Bond Analysis Techniques (ELF and Maximum Probability Domains) Application to a Family of Models Relevant to Bio-Inorganic ChemistryApplications of Density Functional Theory to Biological and Bioinorganic Chemistry
No full textElectron Localization Function (ELF) and Maximum Probability
Domain (MPD) analyses have been applied to model metal–porphyrins and show
compatible and complementary results. ELF basins are quite different from MPDs,
but are a necessary starting point for optimizing them. The analyses of the bond
between the metal and porphyrin do not show significant differences between nontransition
and transition metals. In all the cases considered, we find signatures
characteristic of essentially ionic bonds
L'arche de Noé de Saint-Savin
No full textThe depiction of the ark at Saint-Savin-sur-Gartempe was noted mainly because of the two giant figures holding onto the roof of the ark. Similar representation can be found in the murals of the church of Saint Jean Baptist de Château-Gontier. The author shows their origin to be in Jewish legends. The distribution of the animals and humans in the ark points also to the same origins. The article compares the depiction of the ark in Saint-Savin with those of the illuminations in the manuscripts of the Caedmon poetry, wich shows angels in a somewhat similar position, with the Aelfric paraphrase, as well as the paintings by W. de Brailes, all of which show some traces of Jewish legends. The unconventional form of the sequence and continuity of the stories depicted in the vault painting in the nave of Saint-Savin and the direction of some of the depictions from right to left may point also to an earlier pictorial model of Jewish origin.La représentation de l'arche de Noé à Saint-Savin-sur-Gartempe et son exceptionnelle iconographie ont retenu l'attention des chercheurs essentiellement focalisés sur les deux personnages gigantesques agrippés à la toiture de l'arche. La même représentation figure à l'église Saint-Jean-Baptiste de Château-Gontier. L'A. en fait remonter l'origine aux légendes juives, origine qu'atteste également la distribution des animaux et des hommes aux différents points de l'arche. L'article compare la représentation de l'arche de Saint-Savin, d'une part avec celle des enluminures des manuscrits du poème de Caedmon, où les anges affectent une position quelque peu semblable, d'autre part avec celle de la paraphrase d'Aelfric et des peintures de W. de Brailes, où l'on relève aussi des traces de légendes juives. La forme non conventionnelle des séquences et le fait que la lecture de certaines images se fasse de droite à gauche renvoient aussi à un modèle pictural précoce d'origine juive.Friedman Mira. L'arche de Noé de Saint-Savin. In: Cahiers de civilisation médiévale, 40e année (n°158), Avril-juin 1997. pp. 123-143
Validation and assessment of an accurate approach to the correlation problem in density functional theory: The Kriger–Chen–Iafrate–Savin model
No full textInternational audienceIn the present paper, we validate and assess a correlation functional based on the so-called meta generalized gradient approximation, whose form and parameters are entirely derived only from first-principles criteria. In particular, we have carried out a detailed comparison with the most common, parametrized correlation functionals. Next, we propose a new model in which the correlation functional proposed by Kriger, Chen, Iafrate, and Savin is integrated in a hybrid Hartree-Fock/density functional theory scheme. In such approach only one, or two in the G2-optimized version, parameters are adjusted on experimental data, all the others being derived from purely theoretical considerations. The results obtained for a set of molecular properties, including H-bonded complexes, proton transfer model, SN2 reaction and magnetic properties, are satisfactory and comparable, if not better, with those delivered by the most common functionals including heavy parametrization. The way in which the whole functional is derived and the few empirical parameters used make the new exchange-correlation functional widely applicable
Numerical integration along the adiabatic connection
No full textModel Hamiltonians are used in density functional theory to construct density functional approximations. This technique is now explored without explicitly constructing a density functional, but by only using numerical techniques exploiting known analytical behavior1727.mp4
andreas-savin.mp
Maximum Probability Domains in Crystals: The Rock-Salt Structure
No full textThe present paper studies MX crystals in rock-salt structure (M: Li, Na, K; X: F, Cl, Br, I). They are often described as being formed by ions. Pictures based on quantum mechanical calculations sustain and quantify it. The tools used are (i) the Quantum Theory of Atoms in Molecules, (ii) the Electron Localization Function, and (iii) the maximization of the probability to find in a spatial domain a number of electrons equal to that of the ion under consideration. The present paper shows that the images provided by these three different tools to analyze the quantum mechanical calculations yield, for these systems, very similar results, in the sense that the spatial domains and probability distributions are close. While results for the first two methods are already present in the literature, the last of the methods is applied for the first time to these systems, and details about the method of calculation and program are also given
Maximum Probability Domains in the Solid-State Structures of the Elements: the Diamond Structure
No full textRegions of space are defined to maximize the probability to find two electrons in it. They can be interpreted as regions where Lewis' electron pairs are most likely to be found. These maximum probability domains (MPDs) provide information similar to that obtained from the electron localization function (ELF), but is not identical to it. The elements in the diamond structure provide examples for a comparison
Local and global minimizers for a variational energy involving a fractional norm
No full textWe study existence, uniqueness, and other geometric properties of the minimizers of the energy functional
∥u∥2Hs(Ω)+∫ΩW(u)dx,
where ∥u∥Hs(Ω) denotes the total contribution from Ω in the H s norm of u and W is a double-well potential. We also deal with the solutions of the related fractional elliptic Allen-Cahn equation on the entire space Rn . The results collected here will also be useful for forthcoming papers, where the second and the third author will study the Γ-convergence and the density estimates for level sets of minimizers
Flat level set regularity of p-Laplace phase transitions
No full textWe prove a Harnack inequality for level sets of p-Laplace phase transition minimizers. In particular, if a level set is included in a flat cylinder, then, in the interior, it is included in a flatter one. The extension of a result conjectured by De Giorgi and recently proven by the third author for p = 2 follows
Elliptic boundary value problems associated with isometric group actions
No full textGiven a manifold with boundary endowed with an action of a discrete group on it, we consider the algebra of operators generated by elements in the Boutet de Monvel algebra of pseudodifferential boundary value problems and shift operators acting on functions on the manifold and its boundary. Provided that the group is of polynomial growth and its action is isometric, we construct a Chern character for elliptic elements in this algebra with values in a de Rham type cohomology of the fixed point manifolds for the group action and obtain an index formula in terms of this Chern character. Our index formula contains as special cases the index formula by Fedosov for boundary value problems in the Boutet de Monvel algebra and the index formula by Nazaikinskii, Savin and Sternin for operators on a closed manifold associated with an isometric group action. © 2021, The Author(s), under exclusive licence to Springer Nature Switzerland AG
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No full textEU Telecommunications Law provides a comprehensive overview of the current European regulatory framework as it applies to telecommunications and examines the challenges facing regulators in this sector. Key chapters focus on the selection of appropriate regulatory models that serve to encourage effective investment in next-generation networks and ensure their successful deployment. Andrej Savin provides an up to date overview of all the relevant sources, guiding the reader through these disparate materials in a simple and systematized way. In particular, the book provides analysis of the 2016 proposal for a European Electronic Communications Code (EECC). Using the 2009 Regulatory Framework on electronic communications as a basis the author analyses each of the 2009 framework's five main directives, comparing them with the changes proposed in the EECC. Providing a comprehensive introduction to the main areas of EU telecoms regulation, this book will be of great value to telecoms and IT lawyers. It will also appeal to academics carrying out research in IT law or competition law as it relates to IT and telecoms. EU Telecommunications Law provides a comprehensive overview of the current European regulatory framework as it applies to telecommunications and examines the challenges facing regulators in this sector. Key chapters focus on the selection of appropriate regulatory models that serve to encourage effective investment in next-generation networks and ensure their successful deployment. Andrej Savin provides an up to date overview of all the relevant sources, guiding the reader through these disparate materials in a simple and systematized way. In particular, the book provides analysis of the 2016 proposal for a European Electronic Communications Code (EECC). Using the 2009 Regulatory Framework on electronic communications as a basis the author analyses each of the 2009 framework's five main directives, comparing them with the changes proposed in the EECC. Providing a comprehensive introduction to the main areas of EU telecoms regulation, this book will be of great value to telecoms and IT lawyers. It will also appeal to academics carrying out research in IT law or competition law as it relates to IT and telecoms
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