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Author: Peter Anthonie Kroon
Publisher:
ISBN:
Category :
Languages : en
Pages : 324
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Book Description
Author: Peter Anthonie Kroon
Publisher:
ISBN:
Category :
Languages : en
Pages : 324
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Author: Peter Anthonie Kroon
Publisher:
ISBN:
Category :
Languages : nl
Pages : 138
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Author: Peter Anthonie Kroon
Publisher:
ISBN:
Category : Lattice dynamics
Languages : en
Pages : 148
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Book Description
Author: Martin T. Dove
Publisher: Cambridge University Press
ISBN: 0521392934
Category : Science
Languages : en
Pages : 288
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Book Description
The vibrations of atoms inside crystals - lattice dynamics - is basic to many fields of study in the solid-state and mineral sciences. This book provides a self-contained text that introduces the subject from a basic level and then takes the reader through applications of the theory.
Author: United States. Air Force. Office of Scientific Research
Publisher:
ISBN:
Category : Research
Languages : en
Pages : 1136
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Author: Johan Tidholm
Publisher: Linköping University Electronic Press
ISBN: 9179297595
Category : Electronic books
Languages : en
Pages : 76
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Book Description
The reason to perform calculations in material science usually falls into one of two categories: to predict or explain the origin of material properties. This thesis covers first-principle calculations for solids at extreme conditions, from both of the two mentioned categories. I primarily have studied the effects of high-pressure and high-temperature on lattice dynamics, mechanical and electronic properties. To treat the effects of temperature, ab initio molecular dynamics (AIMD) simulations and self-consistent phonon calculations, based on density functional theory, have been utilised. These approaches account for the temperature effects by considering thermally excited supercells as samples of a statistical ensemble. To extract properties from this representation, I have used methods which maps the supercell data to a unit cell representation or fits it to a simple model Hamiltonian. The small displacement method was used to analyse the dynamical stability for nitrides and polymorphs of silica, synthesised at high-pressure in a diamond anvil cell. The nitride compounds consist of a high amount of nitrogen either as chains, forming a porous framework together with transition metal atoms or as dinitrogen molecules, occupying the channels of the framework. The nitrogen chains consist of single- or double-bonded nitrogen atoms, making these compounds highly energetic. Polymorphs of silica can be used to model deep Earth liquids. These new polymorphs, named coesite-IV and coesite-V, consist of four-, five-, and six-oriented silicon. Some of the octahedra of the six-oriented silicon atoms, of these new phases, are sharing faces, which according to Pauling's third rule would make them highly unstable. My phonon calculations indicate these phases to be dynamically stable. Furthermore, my calculations predict higher compressibility for these new phases compared to the competing ones. By modelling silicate melts with coesite-IV and coesite-V, a more complex and compressible structure is expected, affecting the predicted seismic behaviour. I studied Kohn anomalies for body-centered cubic niobium by simulating this material with self-consistent phonon calculations. The electronic structure was studied by using a band unfolding technique, for which I obtained an effective unit cell representation of the electronic structure at elevated temperatures. Temperature primarily smeared the electronic states but did not induce significant shifts of the bands. In parallel, the anharmonicity of this system was studied using the temperature dependent effective potential method. Even close to the melting temperature, this element is remarkably harmonic. The experimentally observed disappearance of the Kohn anomalies with increased temperature is predominantly dependent, according to my calculations, on the temperature-induced smearing of the electronic states. Using stress-strain relations, accurate high-temperature elastic properties were predicted for Ti0.5Al0.5N. The simulations were performed with AIMD. The stresses were fitted using the least-squares method to a linear expression from which the elastic constants were derived. The results were compared with previously performed calculations that employed additional approximations. The results of the symmetry imposed force constant temperature dependent effective potential (SIFC-TDEP) method agrees well with our results. I also compared my results with TiN calculations that employed a similar methodology. My and the SIFC-TDEP results are reporting lower values for the polycrystalline moduli than the calculations for TiN. The data I generated were also used for a machine learned interatomic potential method, where moment tensor potentials were trained and evaluated, using this data. Den här avhandlingen handlar om beräkningar för material. När materialberäkningar utförs är det antingen för att förutsäga eller förklara egenskaper. De beräkningar som jag har gjort i denna avhandling är baserade på fundamentala fysiska lagar. Detta betyder att de är rent baserade på teori, och inte har anpassats efter resultat av experiment. Jag har i mitt arbete använt mig mycket utav en teori som kallas gitter dynamik. Den är definierad för periodiska material, det vill säga att atomerna i dessa material upprepas i periodiska mönster. Vi kan då anta att det finns en jämviktspunkt för alla atomerna, som de vibrerar omkring. Dessa vibrationer kan beskrivas som om atomerna påverkar varandra med fiktiva fjädrar. Genom att beräkna styrkan för dessa fjädrar kan vi beskriva vibrationerna av atomerna. Dessa vibrationer i sin tur är avgörande för materialets egenskaper. För att beskriva ett material vid en specifik temperatur har jag använt mig utav olika metoder för att simulera det. En simulering kan ses som ett “dator experiment”. Problemet är dock hur vi ska mäta egenskaperna i simuleringen. Ju större och mera komplex en simulering är, desto svårare blir det att beräkna egenskaperna av det simulerade materialet. Vi hamnar i en situation likt den vi skulle befinna oss om vi hade gjort ett experiment i verkligheten, och tvingas använda förenklade modeler för att kunna tolka resultatet. Jag har därför använt mig utav metoder för att utvinna vibrationer av atomer, elektrontillstånd eller elastiska egenskaper, specifikt utvecklade för att användas på denna typ utav simuleringar. Mitt arbete har kretsat kring hur dessa egenskaper påverkas av extrema temperaturer och tryck. De beräkningar jag har utfört vid höga tryck har varit för nyupptäckta nitrider och faser av kiseldioxid. Nitriderna är porösa material som innehåller en stor mängd kväve. Det höga kväveinehållet gör så att det lagras en stor mängd kemisk energi i enkel- och dubbelbindningar mellan kväveatomerna. De nya faserna av kiseldioxid har en betydelse för vår förståelse av jordens inre. Deras existens öppnar upp för att det kan finnas mera komplexa och ihoptryckbara flytande material, under jordens nedre mantel, än vad tidigare har varit antaget. Mina beräkningar har bekräftat strukturerna för dessa nyupptäckta material. Vid höga temperaturer har jag studerat för metallen niob hur vibrationerna av atomerna är relaterade till olika elektrontillstånd. För specifika vibrationer ökar frekvensen med ökad temperatur. Detta är något ovanligt eftersom vibrationernas frekvenser vanligtvis brukar minska med ökad temperatur. Mina simulering för denna metal överensstämmer med resultat från experiment. Orsaken till varför visa vibrationers frekvenser ökar kan jag förklara med att elektrontillståndens enskilda energier varierar över tid på grund av den ökade temperaturen. Jag har även använt mig av simuleringar för att beräkna elastiska egenskaper av legeringen Ti0.5Al0.5N. Ti1?xAlxN legeringar används som beläggningar på skärverktyg som används för metall. För att öka effektiviteten av beläggningen, behövs det detaljerad kunskap av dess mekaniska egenskaper för den temperatur som de används vid. Jag beräknade därför så noggrant som möjligt de elastiska egenskaperna för Ti0.5Al0.5N. Dessa beräkningar är avsedda för att användas som en referens för andra beräkningsmässigt billigare metoder. Datan som genererades från mina simuleringar användes även för en sådan metod, baserad på maskininlärning.
Author: Chick C. Wilson
Publisher: World Scientific
ISBN: 9789810237769
Category : Science
Languages : en
Pages : 390
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Book Description
This important book presents a comprehensive account of the techniques & applications of single crystal neutron diffraction in the area of chemical crystallography & molecular structure. Beginning with a brief description of the general principles & the reasons for choosing the technique - the "why" - the book covers the methods for both the production of neutrons & the measurement of their scattering by molecular crystals - the "how" - followed by a detailed survey of past, present & future applications - the "what". The coverage of both steady state & pulsed neutron sources & instrumentation is extensive, while the survey of applications is the most comprehensive yet undertaken. The book endeavours to show why the technique is an essential method for studying areas as diverse as hydrogen bonding & weak interactions, organometallics, supramolecular chemistry & crystal engineering, metal hydrides, charge density & pharmaceuticals. It is an ideal reference source for the research worker interested in using neutron diffraction to study the structure of molecules. Contents: Crystallography & the Importance of Structural Information; Neutron Scattering; Neutron Diffractometers; Review of Applications I: The Accurate Location of Atoms; Review of Applications II: Hydrogen Bonding & Other Intermolecular Interactions; Review of Applications III: Probing Vibrations & Disorder; Impact on Material Properties & Design; The Future: New Instruments, New Sources, New Techniques. Readership: Students & researchers involved in structural science, especially chemical crystallography.
Author:
Publisher:
ISBN:
Category : Science
Languages : en
Pages : 628
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Author: Surendra K. Saxena
Publisher: Springer Science & Business Media
ISBN: 1461228425
Category : Science
Languages : en
Pages : 380
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Book Description
With the rapid development of fast processors, the power of a mini-super computer now exists in a lap-top box. Quite sophisticated techniques are be coming accessible to geoscientists, thus making disciplinary boundaries fade. Chemists and physicists are no longer shying away from computational mineral ogical and material science problems "too complicated to handle." Geoscientists are willing to delve into quantitative physico-chemical methods and open those "black boxes" they had shunned for several decades but with which had learned to live. I am proud to present yet another volume in this series which is designed to break the disciplinary boundaries and bring the geoscientists closer to their chemist and physicist colleagues in achieving a common goal. This volume is the result of an international collaboration among many physical geochemists (chemists, physicists, and geologists) aiming to understand the nature of material. The book has one common theme: namely, how to determine quantitatively through theory the physico-chemical parameters of the state of a solid or fluid.
Author: R. F. Wallis
Publisher: Elsevier
ISBN: 1483223418
Category : Science
Languages : en
Pages : 747
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Book Description
Lattice Dynamics covers the proceedings of the 1963 International Conference on Lattice Dynamics, held at the H.C. Ørsted Institute of the University of Copenhagen on August 5-9. This book is composed of seven parts that focus on a better fundamental understanding of the interactions between atoms in solids and their role in lattice dynamics. The major topics covered include phonon dispersion curves, anharmonic effects, optical and dielectric effects, influence of defects on lattice vibrations, elasticity, and developments. Papers on the study of vibrational spectra by infrared absorption, X-ray and neutron scattering and the electron tunneling effects as well as papers on the influence of defects and on a variety of other problems in lattice dynamics are included. This book will prove useful to applied physicists and researchers in the field and related fields of lattice dynamics.
