Recent developments in density functional theory (DFT) methods applicable to studies of large periodic systems are outlined. During the past three decades, DFT has become an essential part of computational materials science, addressing problems in materials design and processing. The theory allows us to interpret experimental data and to generate property data (such as binding energies of molecules on surfaces) for known materials, and also serves as an aid in the search for and design of novel materials and processes. A number of algorithmic implementations are currently being used, including ultrasoft pseudopotentials, efficient iterative schemes for solving the one-electron DFT equations, and computationally efficient codes for massively parallel computers. The first part of this article provides an overview of plane-wave pseudopotential DFT methods. Their capabilities are subsequently illustrated by examples including the prediction of crystal structures, the study of the compressibility of minerals, and applications to pressure-induced phase transitions. Future theoretical and computational developments are expected to lead to improved accuracy and to treatment of larger systems with a higher computational efficiency. c 2000 John Wiley & Sons, Inc. Int J Quant Chem 77: 895-910, 2000

/pdf/electronic-structure-properties-and-phase-stability-of-2addststx9.pdf

Electronic structure, properties, and phase stability of inorganic crystals: A pseudopotential plane-wave study

The calculation of the electronic properties of materials is an important task of solid-state theory, albeit particularly difficult if electronic correlations are strong, e.g., in transition metals, their oxides and in f-electron systems. The standard approach to material calculations, the density functional theory in its local density approximation (LDA), incorporates electronic correlations only very rudimentarily and fails if the correlations are strong. Encouraged by the success of dynamical mean field theory (DMFT) in dealing with strongly correlated model Hamiltonians, physicists from the bandstructure and the many-body communities have joined forces and developed a combined LDA + DMFT method recently. Depending on the strength of electronic correlations, this new approach yields a weakly correlated metal as in the LDA, a strongly correlated metal or a Mott insulator. This approach is widely regarded as a breakthrough for electronic structure calculations of strongly correlated materials. We review ...

Electronic structure calculations using dynamical mean field theory

Actinide elements produce a plethora of interesting physical behaviors due to the $5f$ states. This review compiles and analyzes progress in the understanding of the electronic and magnetic structure of the $5f$ states in actinide metals. Particular interest is given to electron energy-loss spectroscopy and many-electron atomic spectral calculations, since there is now an appreciable library of core $d\ensuremath{\rightarrow}\text{valence}$ $f$ transitions for Th, U, Np, Pu, Am, and Cm. These results are interwoven and discussed against published experimental data, such as x-ray photoemission and absorption spectroscopy, transport measurements, and electron, x-ray, and neutron diffraction, as well as theoretical results, such as density-functional theory and dynamical mean-field theory.

Nature of the 5f states in actinide metals

Diamond-anvil-cell and shock-wave technologies now permit the study of matter under multimegabar pressure (that is, of several hundred GPa). The properties of matter in this pressure regime differ drastically from those known at 1 atm (about 105 Pa). Just how different chemistry is at high pressure and what role chemical intuition for bonding and structure can have in understanding matter at high pressure will be explored in this account. We will discuss in detail an overlapping hierarchy of responses to increased density: a) squeezing out van der Waals space (for molecular crystals); b) increasing coordination; c) decreasing the length of covalent bonds and the size of anions; and d) in an extreme regime, moving electrons off atoms and generating new modes of correlation. Examples of the startling chemistry and physics that emerge under such extreme conditions will alternate in this account with qualitative chemical ideas about the bonding involved.

The chemical imagination at work in very tight places.

Ceria and its solid solutions play a vital role in several industrial processes and devices. These include solar energy-to-fuel conversion, solid oxide fuel and electrolyzer cells, memristors, chemical looping combustion, automotive 3-way catalysts, catalytic surface coatings, supercapacitors and recently, electrostrictive devices. An attractive feature of ceria is the possibility of tuning defect-chemistry to increase the effectiveness of the materials in application areas. Years of study have revealed many features of the long-range, macroscopic characteristics of ceria and its derivatives. In this review we focus on an area of ceria defect chemistry which has received comparatively little attention - defect-induced local distortions and short-range associates. These features are non-periodic in nature and hence not readily detected by conventional X-ray powder diffraction. We compile the relevant literature data obtained by thermodynamic analysis, Raman spectroscopy, and X-ray absorption fine structure (XAFS) spectroscopy. Each of these techniques provides insight into material behavior without reliance on long-range periodic symmetry. From thermodynamic analyses, association of defects is inferred. From XAFS, an element-specific probe, local structure around selected atomic species is obtained, whereas from Raman spectroscopy, local symmetry breaking and vibrational changes in bonding patterns is detected. We note that, for undoped ceria and its solid solutions, the relationship between short range order and cation-oxygen-vacancy coordination remains a subject of active debate. Beyond collating the sometimes contradictory data in the literature, we strengthen this review by reporting new spectroscopy results and analysis. We contribute to this debate by introducing additional data and analysis, with the expectation that increasing our fundamental understanding of this relationship will lead to an ability to predict and tailor the defect-chemistry of ceria-based materials for practical applications.

/pdf/a-review-of-defect-structure-and-chemistry-in-ceria-and-its-5g7hh8z7wn.pdf

A review of defect structure and chemistry in ceria and its solid solutions

High-pressure X-ray diffraction studies have been performed on cerium powder up to 46 GPa using a diamond anvil cell and synchrotron radiation. The results confirm the following transitions: γ(fcc)−α(fcc) at 0.8 GPa, α(fcc)−α″ (monoclinic b.c.) at 5 GPa and α″ (monoclinic bc)-tetragonal bc at 12 GPa. All high-pressure structures can be described as distorted fcc. No clear evidence has been found for the α'-phase with α-uranium structure. It is found that the bulk modulus is 21 GPa for γ-Ce and 20 GPa for the combined compression data of α−Ce, α″-Ce and tetragonal Ce in good agreement with other experimental and theoretical data. The experimental V(P) data are compared with a theoretical equation of state obtained by the linear muffin-tin method.

The crystal structure and the equation of state of cerium metal in the pressure range 0–46 Gpa

Comparative aspects of the high-pressure behaviour of lanthanide and actinide compounds

Low-temperature resistance measurements were performed on UTe crystals in the pressure range from 1 GPa to 20 GPa The Curie temperature obtained as the maximum in the temperature derivative dR/dT, increases strongly with pressure It has a maximum at 75 GPa followed by a decrease with a smaller slope at higher pressures Another anomaly in the R-T characteristic is observed above 10 GPa and ascribed to the presence of the B2 phase, which is known to form in a very sluggish phase transformation

http://iopscience.iop.org/article/10.1088/0953-8984/4/25/011/pdf

High-pressure resistance study of UTe

High-pressure X-ray diffraction studies have been performed on UN powder for pressures up to 34 GPa using synchrotron radiation and a diamond anvil cell. For the cubic low-pressure phase the bulk modulus B0 equals 203(6) GPa and its pressure derivative B′0 equals 6.3(6) in good agreement with other data from the literature. The UN material has been found to transform to a new phase, UN III, at 29 GPa. The transformation is first order with a 3.2% decrease in volume. The UN III phase has been indexed according to a face-centred rhombohedral cell with a = 4.657(5) A and α = 85.8(2)° at 34 GPa. The influence of the 5f electrons in the transformation is discussed.

A new high-pressure phase of uranium nitride studied by X-ray diffraction and synchrotron radiation

Thorium and plutonium dioxides were studied under pressure by the energy dispersive X-ray diffraction method. A double conical slit assembly was used to collect simultaneously the diffracted radiation at five and seven degrees. ThO2 undergoes a phase transformation at 40 GPa. The high-pressure phase remains stable up to 55 GPa, the highest pressure reached in the experiment. For PuO2, a structural transformation occurs near 39 GPa. The observed high-pressure phases of ThO2 and PuO2 exhibit similar diffraction spectra. Like for some other fluorite type compounds, the ThO2 and PuO2 high-pressure phase has been indexed in the PbCl2-type structure. The bulk modulus has been calculated as B0= 262 GPa with a pressure derivative of B0' = 6.7 for ThO2 and as B0 = 379 GPa with B0' = 2.4 for PuO2. The volume decrease at the transition is 12% for PuO2 and 8% for ThO2.

Pressure-induced phase transition in ThO2 and PuO2

Handle everyday research tasks with reliable, citation-backed results

Your personal Research Agent to handle research tasks with citation-backed results

Popular Tasks used by Researchers

How can I help with your research?

Meet SciSpace

Get more enhanced response by uploading the PDFs you want me to reference.

No relevant PDFs in your library

SciSpace is the AI research assistant for academics. Run systematic literature reviews on 280M+ papers, and write papers with cited sources. Trusted by 1M+ students, PhDs & researchers.

SciSpace | AI for Research

Analyze PDFs

Code & Manuscripts

Funding & Grants

Literature & Patents

Medical & Clinical Data

Systematic Review

Visualize & Present

Web & Data

Build a Google Scholar-like website for your research.

Build a website

Create charts and images for your research

Create a Chart

Write a paper for submission to a journal

Draft a manuscript

Patent Search

Design eye-catching scientific posters in minutes.

Scientific Poster Generation

Systematic Literature Review

One task is running at the moment. Your messages will be shown right after.

Drag and drop or click here to browse

Loved by <highlight>1 million+</highlight> researchers

Extract a list of specific topics and their sources from unstructured text

Topics

Compare and analyze relevant papers that matches with your search

Papers

Get insights from PDFs and bookmarked papers from your library

My library

Recent searches

Try searching for:

Catch AI-generated content in scholarly and non-scholarly content

{ai} Detector

Ai Writer

Get PDF Summaries, highlighted text explanations 

Chat with PDF

Effortlessly create in-text citations and bibliographies in APA and 2,500 other formats

Citation generator

Get explanations, summaries, and answers on academic papers

Ease up your research workflow with {scispace}'s cohort of exciting AI tools

Elevate your academic writing skills and convey your ideas the way you want

Paraphraser

Explore our range of reading and writing tools

Your file is being prepared and should be ready in a few minutes. If it's a large file, it might take a bit longer. You can close this window, and we'll email you the file when it's done.

You have reached a maximum limit of <strong>{limit}</strong> columns in the table. Remove at least <strong>1</strong> column to add or create another one.

U. Benedict

Author Tools

Chat about Author