243,040 research outputs found
Inclusion of Experimental Information in First Principles Modeling of Materials
We propose a novel approach to model amorphous materials using a first
principles density functional method while simultaneously enforcing agreement
with selected experimental data. We illustrate our method with applications to
amorphous silicon and glassy GeSe. The structural, vibrational and
electronic properties of the models are found to be in agreement with
experimental results. The method is general and can be extended to other
complex materials.Comment: 11 pages, 8 PostScript figures, submitted to J. Phys.: Condens.
Matter in honor of Mike Thorpe's 60th birthda
Energy scaling law for nanostructured materials
The equilibrium binding energy is an important factor in the design of
materials and devices. However, it presents great computational challenges for
materials built up from nanostructures. Here we investigate the binding-energy
scaling law from first-principles calculations. We show that the equilibrium
binding energy per atom between identical nanostructures can scale up or down
with nanostructure size. From the energy scaling law, we predict finite
large-size limits of binding energy per atom. We find that there are two
competing factors in the determination of the binding energy: Nonadditivities
of van der Waals coefficients and center-to-center distance between
nanostructures. To uncode the detail, the nonadditivity of the static multipole
polarizability is investigated. We find that the higher-order multipole
polarizability displays ultra-strong intrinsic nonadditivity, no matter if the
dipole polarizability is additive or not.Comment: 13 pages, 4 figures, 7 table
Recommended from our members
Misunderstanding Models in Environmental and Public Health Regulation
Computational models are fundamental to environmental regulation, yet their capabilities tend to be misunderstood by policymakers. Rather than rely on models to illuminate dynamic and uncertain relationships in natural settings, policymakers too often use models as “answer machines.” This fundamental misperception that models can generate decisive facts leads to a perverse negative feedback loop that begins with policymaking itself and radiates into the science of modeling and into regulatory deliberations where participants can exploit the misunderstanding in strategic ways. This paper documents the pervasive misperception of models as truth machines in U.S. regulation and the multi-layered problems that result from this misunderstanding. The paper concludes with a series of proposals for making better use of models in environmental policy analysis.The Kay Bailey Hutchison Center for Energy, Law, and Busines
Network destabilization and transition in depression : new methods for studying the dynamics of therapeutic change
The science of dynamic systems is the study of pattern formation and system change. Dynamic systems theory can provide a useful framework for understanding the chronicity of depression and its treatment. We propose a working model of therapeutic change with potential to organize findings from psychopathology and treatment research, suggest new ways to study change, facilitate comparisons across studies, and stimulate treatment innovation. We describe a treatment for depression that we developed to apply principles from dynamic systems theory and then present a program of research to examine the utility of this application. Recent methodological and technological developments are also discussed to further advance the search for mechanisms of therapeutic change
Realistic Modeling of Complex Oxide Materials
Since electronic and magnetic properties of many transition-metal oxides can
be efficiently controlled by external factors such as the temperature,
pressure, electric or magnetic field, they are regarded as promising materials
for various applications. From the viewpoint of electronic structure, these
phenomena are frequently related to the behavior of a small group of states
close to the Fermi level. The basic idea of this project is to construct a
low-energy model for the states near the Fermi level on the basis of
first-principles density functional theory, and to study this model by modern
many-body techniques. After a brief review of the method, the abilities of this
approach will be illustrated on a number of examples, including multiferroic
manganites and spin-orbital-lattice coupled phenomena in RVO3 (R being the
three-valent element).Comment: 3 pages, 6 figures, Conference on Computational Physics 200
Ab initio atomistic thermodynamics and statistical mechanics of surface properties and functions
Previous and present "academic" research aiming at atomic scale understanding
is mainly concerned with the study of individual molecular processes possibly
underlying materials science applications. Appealing properties of an
individual process are then frequently discussed in terms of their direct
importance for the envisioned material function, or reciprocally, the function
of materials is somehow believed to be understandable by essentially one
prominent elementary process only. What is often overlooked in this approach is
that in macroscopic systems of technological relevance typically a large number
of distinct atomic scale processes take place. Which of them are decisive for
observable system properties and functions is then not only determined by the
detailed individual properties of each process alone, but in many, if not most
cases also the interplay of all processes, i.e. how they act together, plays a
crucial role. For a "predictive materials science modeling with microscopic
understanding", a description that treats the statistical interplay of a large
number of microscopically well-described elementary processes must therefore be
applied. Modern electronic structure theory methods such as DFT have become a
standard tool for the accurate description of individual molecular processes.
Here, we discuss the present status of emerging methodologies which attempt to
achieve a (hopefully seamless) match of DFT with concepts from statistical
mechanics or thermodynamics, in order to also address the interplay of the
various molecular processes. The new quality of, and the novel insights that
can be gained by, such techniques is illustrated by how they allow the
description of crystal surfaces in contact with realistic gas-phase
environments.Comment: 24 pages including 17 figures, related publications can be found at
http://www.fhi-berlin.mpg.de/th/paper.htm
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