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Artykuły w czasopismach na temat "Density Functional Theory (DFT) - First Principles Calculations"
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Wang, Yuqiu, Binkai Yu, Jin Xiao, Limin Zhou i Mingzhe Chen. "Application of First Principles Computations Based on Density Functional Theory (DFT) in Cathode Materials of Sodium-Ion Batteries". Batteries 9, nr 2 (27.01.2023): 86. http://dx.doi.org/10.3390/batteries9020086.
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Sodium-ion batteries (SIBs) have been widely explored by researchers because of their abundant raw materials, uniform distribution, high-energy density and conductivity, low cost, and high safety. In recent years, theoretical calculations and experimental studies on SIBs have been increasing, and the applications and results of first-principles calculations have aroused extensive interests worldwide. Herein, the authors review the applications of density functional (DFT) theory in cathode materials for SIBs, summarize the applications of DFT in transition-metal oxides/chalcogenides, polyanionic compounds, Prussian blue, and organic cathode materials for SIBs from three aspects: diffusion energy barrier and diffusion path, energy calculation and structure, and electronic structure. The relationship between the structure and performance of the battery material will be comprehensively understood by analyzing the specific working principle of battery material through theoretical calculation and combining with high-precision experimental characterization technologies. Selecting materials with good performance from a large number of electrode materials through theoretical calculation can avoid unnecessary complex experiments and instrument characterizations. With the gradual deepening of research, the DFT calculation will play a greater role in the sodium-ion battery electrode field.
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Hashir, P., P. P. Pradyumnan, Aadil Fayaz Wani i Kulwinder Kaur. "Experimental and First-Principles Thermoelectric studies of Bulk ZnO". IOP Conference Series: Materials Science and Engineering 1263, nr 1 (1.10.2022): 012025. http://dx.doi.org/10.1088/1757-899x/1263/1/012025.
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The Thermoelectric perspective to produce electricity from waste heat has obtained great attention over the last few years. However, the fulfillment of energy requirement of the contemporary world by the thermoelectric method can be achieved by developing good thermoelectric materials of high conversion efficiency. Density functional theory (DFT) is widely used simulation technique in the materials science field for computing electronic properties of the materials. In our DFT calculation Quantum Espresso (QE) package were used to investigate the electronic band structure as well as electronic density of states of bulk ZnO sample. To express core electrons, projector-augmented wave (PAW) pseudopotentials were chosen and to optimize band structure LDA+U method of DFT approximation was opted. Our DFT calculations give direct band gap 3.2004 eV and the experimental value is 3.24 eV. Our works are found to be good acceptance with previously reported values and the DFT study via QE and BoltzTraP codes are suitable for predicting the thermoelectric properties of semiconductor materials.
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Ali, Abdelnabi. "Electronic and magnetic proprieties of NiO surfaces from first-principles". FES Journal of Engineering Sciences 11, nr 1 (18.01.2022): 37–42. http://dx.doi.org/10.52981/fjes.v11i1.1732.
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Density functional theory (DFT) is used to study the electronic and magnetic properties of different surfaces of NiO. The electronic and magnetic properties of forming different surfaces of Nicoles such as (001), (110), (101), and (111) were studied using density functional theory calculations from the first principle used. Our result found that the band gap changed dramatically, and the spin projected density of state changed the dominations of the majority and minority of spin channels around the Fermi level, and the charge density of the bulk and NiO (111) surface is also discussed. However, the magnetic properties observed the increasing and decreasing spin magnetic moments and found significant magnetic moments for O atoms in the NiO (101) slab. These features lead to a surprisingly diverse set of different surface electronic structures. The study observed that DFT + U density functional theory might be a valuable method for high-throughput workflows that require reliable band gap predictions at a moderate computational cost.
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Sarmadian, Nasrin, Rolando Saniz, Bart Partoens, Dirk Lamoen, Kalpana Volety, Guido Huyberechts i Johan Paul. "High throughput first-principles calculations of bixbyite oxides for TCO applications". Phys. Chem. Chem. Phys. 16, nr 33 (2014): 17724–33. http://dx.doi.org/10.1039/c4cp02788d.
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We present a high-throughput computing scheme based on density functional theory (DFT) to generate a class of oxides and screen them with the aim of identifying those that might be electronically appropriate for transparent conducting oxide (TCO) applications.
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Xia, Lu, Thomas Tybell i Sverre M. Selbach. "Bi vacancy formation in BiFeO3 epitaxial thin films under compressive (001)-strain from first principles". Journal of Materials Chemistry C 7, nr 16 (2019): 4870–78. http://dx.doi.org/10.1039/c8tc06608f.
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Teng, Tsung-Fan, Santhanamoorthi Nachimuthu, Wei-Hsiu Hung i Jyh-Chiang Jiang. "A first principles study of H2S adsorption and decomposition on a Ge(100) surface". RSC Advances 5, nr 5 (2015): 3825–32. http://dx.doi.org/10.1039/c4ra08887e.
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Usseinov, Abay, Zhanymgul Koishybayeva, Alexander Platonenko, Vladimir Pankratov, Yana Suchikova, Abdirash Akilbekov, Maxim Zdorovets, Juris Purans i Anatoli I. Popov. "Vacancy Defects in Ga2O3: First-Principles Calculations of Electronic Structure". Materials 14, nr 23 (2.12.2021): 7384. http://dx.doi.org/10.3390/ma14237384.
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First-principles density functional theory (DFT) is employed to study the electronic structure of oxygen and gallium vacancies in monoclinic bulk β-Ga2O3 crystals. Hybrid exchange–correlation functional B3LYP within the density functional theory and supercell approach were successfully used to simulate isolated point defects in β-Ga2O3. Based on the results of our calculations, we predict that an oxygen vacancy in β-Ga2O3 is a deep donor defect which cannot be an effective source of electrons and, thus, is not responsible for n-type conductivity in β-Ga2O3. On the other hand, all types of charge states of gallium vacancies are sufficiently deep acceptors with transition levels more than 1.5 eV above the valence band of the crystal. Due to high formation energy of above 10 eV, they cannot be considered as a source of p-type conductivity in β-Ga2O3.
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Muhammad, Rafique, Yong Shuai i He-Ping Tan. "A first-principles study on alkaline earth metal atom substituted monolayer boron nitride (BN)". Journal of Materials Chemistry C 5, nr 32 (2017): 8112–27. http://dx.doi.org/10.1039/c7tc02894f.
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This paper presents first-principles density functional theory (DFT) calculations for the structural, electronic, magnetic and optical properties of monolayer boron nitride (BN) doped with different alkaline earth metal (AEM) atoms.
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Pulido, Ruth, Nelson Naveas, Raúl J. Martin-Palma, Fernando Agulló-Rueda, Victor R. Ferró, Jacobo Hernández-Montelongo, Gonzalo Recio-Sánchez, Ivan Brito i Miguel Manso-Silván. "Phonon Structure, Infra-Red and Raman Spectra of Li2MnO3 by First-Principles Calculations". Materials 15, nr 18 (8.09.2022): 6237. http://dx.doi.org/10.3390/ma15186237.
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The layer-structured monoclinic Li2MnO3 is a key material, mainly due to its role in Li-ion batteries and as a precursor for adsorbent used in lithium recovery from aqueous solutions. In the present work, we used first-principles calculations based on density functional theory (DFT) to study the crystal structure, optical phonon frequencies, infra-red (IR), and Raman active modes and compared the results with experimental data. First, Li2MnO3 powder was synthesized by the hydrothermal method and successively characterized by XRD, TEM, FTIR, and Raman spectroscopy. Secondly, by using Local Density Approximation (LDA), we carried out a DFT study of the crystal structure and electronic properties of Li2MnO3. Finally, we calculated the vibrational properties using Density Functional Perturbation Theory (DFPT). Our results show that simulated IR and Raman spectra agree well with the observed phonon structure. Additionally, the IR and Raman theoretical spectra show similar features compared to the experimental ones. This research is useful in investigations involving the physicochemical characterization of Li2MnO3 material.
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Gawai, U. P., U. P. Deshpande i B. N. Dole. "A study on the synthesis, longitudinal optical phonon–plasmon coupling and electronic structure of Al doped ZnS nanorods". RSC Advances 7, nr 20 (2017): 12382–90. http://dx.doi.org/10.1039/c6ra28180j.
Pełny tekst źródłaRozprawy doktorskie na temat "Density Functional Theory (DFT) - First Principles Calculations"
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Cankurtaran, Burak O. "Linear-scaling techniques for first principles calculations of stationary and dynamic systems". Thesis, Curtin University, 2010. http://hdl.handle.net/20.500.11937/24.
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First principles calculations can be a computationally intensive task when studying large systems. Linear-scaling methods must be employed to find the electronic structure of systems consisting of thousands of atoms and greater. The goal of this thesis is to combine the linear-scaling divide-and-conquer (D&C) method with the linear-scaling capabilities of the SIESTA (Spanish Initiative for Electronic Simulations with Thousands of Atoms) density functional theory (DFT) methodology and present this union as a viable approach to large-scale first principles calculations. In particular, the density matrix version of the D&C method is implemented into the SIESTA package. This implementation can accommodate high quality calculations consisting of atom numbers in the tens of thousands using moderate computing resources. Low quality calculations have been tested up to half million atoms using reasonably sized computing resources.The D&C method is extended to better handle atomic dynamics simulations. First, by alleviating issues caused by discontinuities in the potential energy surface, with the application of a switching function on the Hamiltonian and overlap matrices. This allows for a smooth potential energy surface to be generated. The switching function has the additional benefit of accelerating the self-consistent field (SCF) process. Secondly, the D&C frozen density matrix (FDM) is modified to allow for improved charge transfer between the active and constrained regions of the system. This modification is found to reduce both the number of SCF iterations required for self-consistency and the number of relaxation steps in a local geometry optimisation. The D&C paradigm is applied to the real-time approach of time-dependent density functional theory (TDDFT). The method is tested on a linear alkane molecule with varying levels of success.Divergences in the induced dipole moment occur when the external excitation field is aligned parallel to the axis of the molecule. The method succeeds in producing accurate dipole moments when the external field is aligned perpendicular to the molecule. Various techniques are tested to improve the proposed method. Finally, the performance and effectiveness of the current D&C implementation is evaluated by studying three current systems. The first two systems consist of two different DNA sequences and the last system is the large ZIF-100 zeolitic imidazolate framework (ZIF).
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Gidby, Marcus. "Defects in ceria". Thesis, Linköping University, Department of Physics, Chemistry and Biology, 2009. http://urn.kb.se/resolve?urn=urn:nbn:se:liu:diva-17576.
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The solid oxide fuel cell (SOFC) technology has been under research since thelate 1950s, and most of the research has been on designs utilizing yttria stabilized zirconia (YSZ) as the electrolyte of choice. However, the SOFC technology has the major drawback of requiring high operation temperatures (up to 1000 degrees Celcius), so research of alternative materials have come into interest that would possibly require a lower working temperature without any significant loss of conductivity.One such material of interest for the electrolyte is compounds of ceriumdioxide (ceria). Ceria is well known for its ability to release oxygen by formingoxygen vacancies under oxygen-poor conditions, which increases its oxygen ionconductivity, and works at a lower temperature than the YSZ compounds whenproperly doped. Conversely, ceria is also able to absorb oxygen under oxygen-rich conditions, and those two abilities make it a very good material to use in catalytic converters for reduction of carbon monoxide and nitrogen oxide emission. The ability for the oxygen ions to easily relocate inbetween the different lattice sites is likely the key property of oxygen ion transportation in ceria. Also, in oxygen-rich conditions, the absorbed oxygen atom is assumed to join the structure at either the roomy octrahedral sites, or the vacant tetrahedral sites. Following that, the oxygen atom may relocate to other vacant locations, given it can overcome a possible potential barrier.
This thesis studies how those interstitial oxygen vacancies (defects) affect theenergy profile of ceria-based supercells by first principles calculations. The system is modeled within the density functional theory (DFT) with aid of (extended) local density approximation (LDA+U) using the software VASP. Furthermore, it is studied how those vacancies affect neighbouring oxygen atoms, and wether or not it is energetically benificial for the neighbouring atoms to readjust their positions closer or further away from the vacancy. The purpose of this thesis is to analyze wether or not it is theoretically possible that interstitial oxygen vacancies may cause neighbouring oxygen atoms to naturally relocate to the octahedral site in ceria, and how this affects the overall energy profile of the material.
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Youssef, Srour Juliana. "Structure électronique et compétition de phases dans les semi-conducteurs Cu-(In,Ga)-Se, Ga-Se et In-Se : calculs premiers principes basés sur divers potentiels d'échange-corrélation". Thesis, Université de Lorraine, 2016. http://www.theses.fr/2016LORR0238/document.
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Afin de pouvoir utiliser les nouveaux matériaux semi-conducteurs dans les domaines de l’électronique et de l’optique, il faut parvenir à comprendre leur «structure électronique», ou plus précisément le positionnement des niveaux d’énergie des électrons impliqués dans l’absorption / émission d’un photon. Les propriétés électroniques, sensibles à la composition chimique et à la structure du matériau, sont théoriquement accessibles en résolvant les équations de la mécanique quantique sur ordinateur. Ce travail porte sur des simulations théoriques de la structure électronique de semi-conducteurs binaires constitués d'indium (ou du gallium) et de sélénium, ainsi que de leurs "dérivés" à base de cuivre. La stabilité relative des phases cristallographiques de certains composés In-Se et Ga-Se a été évaluée, ce qui a permis d’expliquer certaines tendances connues et de formuler des prédictions. Les résultats obtenus seront particulièrement utiles dans le domaine du photovoltaïque. Les simulations numériques ont été réalisées dans le cadre de la théorie de la fonctionnelle de la densité (DFT), visant les structures cristallines d'équilibre et les propriétés électroniques de quelques semi-conducteurs binaires ou (pseudo)ternaires à base de Cu, In, Ga et Se. Les systèmes étudiés possèdent la même structure à courte portée (environnement tétraédrique des cations et anions) mais diffèrent à longue portée. Les composés binaires (Ga/In)Se, (Ga/In)2Se3 constituent des références importantes dans les diagrammes de phases des systèmes à base de (Cu, In, Se) et (Cu, Ga, Se), au sein desquels figurent les phases potentiellement utiles dans le domaine du photovoltaïque. Le travail comprend deux chapitres d'introduction et trois chapitres exposant des résultats nouveauxIn order to optimally use new semiconductor materials in electronics or optics, one needs to understand their “electronic structure”, that is, the mutual placement of the electron energy levels concerned by the processes of absorption / emission of a photon. The electronic properties, which depend on the material’s chemical composition and crystal structure, may be assessed by theory via solving quantum-mechanical equations on a computer. The present work deals with theory simulations of electronic structure done for several binary semiconductors consisting of indium (or gallium) and selenium, moreover for their “derivatives” containing copper. As a result, the relative stability of crystallographic phases of some Ga-Se and In-Se compounds has been assessed, explaining the known trends and making predictions. The results are expected to be useful for current works in photovoltaics. The numerical simulations have been performed within the density functional theory (DFT), aimed at the equilibrium crystal structures and electronic characteristics of several binary or (pseudo)ternary semiconductors based on Cu, In, Ga and Se. The compounds under study share similar short-range order features (tetrahedral environment of both cations and anions), differently assembled on a long-range scale. The binary compounds (Ga/In)Se, (Ga/In)2Se3 mark important end points at the phase diagrams of the (Cu,In,Se) and (Cu,Ga,Se) systems that cover a number of phases relevant, e.g., for applications in photovoltaics. The work comprises two chapters of introduction and three outlining novel results
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Villanova, John William. "Examining Topological Insulators and Topological Semimetals Using First Principles Calculations". Diss., Virginia Tech, 2018. http://hdl.handle.net/10919/82959.
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The importance and promise that topological materials hold has been recently underscored by the award of the Nobel Prize in Physics in 2016 ``for theoretical discoveries of topological phase transitions and topological phases of matter." This dissertation explores the novel qualities and useful topologically protected surface states of topological insulators and semimetals.
Topological materials have protected qualities which are not removed by weak perturbations. The manifestations of these qualities in topological insulators are spin-momentum-locked surface states, and in Weyl and Dirac semimetals they are unconventional open surface states (Fermi arcs) with anomalous electrical transport properties. There is great promise in utilizing the topologically protected surface states in electronics of the future, including spintronics, quantum computers, and highly sensitive devices. Physicists and chemists are also interested in the fundamental physics and exotic fermions exhibited in topological materials and in heterostructures including them.
Chapter 1 provides an introduction to the concepts and methods of topological band theory. Chapter 2 investigates the spin and spin-orbital texture and electronic structures of the surface states at side surfaces of a topological insulator, Bi2Se3, by using slab models within density functional theory. Two representative, experimentally achieved surfaces are examined, and it is shown that careful consideration of the crystal symmetry is necessary to understand the physics of the surface state Dirac cones at these surfaces. This advances the existing literature by properly taking into account surface relaxation and symmetry beyond what is contained in effective bulk model Hamiltonians.
Chapter 3 examines the Fermi arcs of a topological Dirac semimetal (DSM) in the presence of asymmetric charge transfer, of the kind which would be present in heterostructures. Asymmetric charge transfer allows one to accurately identify the projections of Dirac nodes despite the existence of a band gap and to engineer the properties of the Fermi arcs, including spin texture. Chapter 4 investigates the effect of an external magnetic field applied to a DSM. The breaking of time reversal symmetry splits the Dirac nodes into topologically charged Weyl nodes which exhibit Fermi arcs as well as conventionally-closed surface states as one varies the chemical potential.Ph. D.
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Nicholson, Kelly Marie. "First principles calculations of thermodynamics of high temperature metal hydrides for NGNP applications". Diss., Georgia Institute of Technology, 2014. http://hdl.handle.net/1853/54027.
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In addition to their potential use at low to moderate temperatures in mobile fuel cell technologies, metal hydrides may also find application as high temperature tritium getterers in the U.S. DOE Next Generation Nuclear Plant (NGNP). We use Density Functional Theory to identify metal hydrides capable of sequestering tritium at temperatures in excess of 1000 K. First we establish the minimum level of theory required to accurately capture the thermodynamics of highly stable metal hydrides and determine that isotope effects can be neglected for material screening. Binary hydride thermodynamics are largely well established, and ternary and higher hydrides typically either do not form or decompose at lower temperatures. In this thesis we investigate anomalous systems with enhanced stability in order to identify candidates for the NGNP application beyond the binary hydrides. Methods implemented in this work are particularly useful for deriving finite temperature phase stability behavior in condensed systems. We use grand potential minimization methods to predict the interstitial Th−Zr−H phase diagram and apply high throughput, semi-automated screening methodologies to identify candidate complex transition metal hydrides (CTMHs) from a diverse library of all known, simulation ready ternary and quaternary CTMHs (102 materials) and 149 hypothetical ternary CTMHs based on existing prototype structures. Our calculations significantly expand both the thermodynamic data available for known CTMHs and the potential composition space over which previously unobserved CTMHs may be thermodynamically stable. Initial calculations indicate that the overall economic viability of the tritium sequestration system for the NGNP will largely depend on the amount of protium rather than tritium in the metal hydride gettering bed feed stream.
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Cheng, Lei. "FIRST-PRINCIPLES DENSITY FUNCTIONAL THEORY STUDIES OF REACTIVITIES OF HETEROGENEOUS CATALYSTS DETERMINED BY STRUCTURE AND SUBSTRATE". OpenSIUC, 2009. https://opensiuc.lib.siu.edu/dissertations/99.
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In this dissertation, density functional theory (DFT) calculations were used to investigate (1)NO2 adsorption on BaO in NOx Storage Reduction (NSR) catalyst affected by the morphology of BaO and the γ-Al2O3 support, (2) energy barrier of H2 dissociative adsorption over Mg clusters affected by its electronic structure, and (3) comparison of the activities of CeO2 clusters affected by two different supports--monoclinic ZrO2 and non-spinel γ-Al2O3. Our results showed that the electronic effect caused by the non-stoichiometry of the bare BaO clusters and surfaces improves their reactivities toward NO2 adsorption greatly, whereas the geometric structure of the catalyst has only minor effect on the activity; we also found that the γ-Al2O3 substrate improves the reactivities of the supported BaO clusters and at the same time the interface between BaO and γ-Al2O3 provided a unique and highly reactive environment for NO2 adsorption. Hydrogen dissociation barrier over pure Mg clusters is greatly affected by the electronic structure of the clusters--closed shell clusters such as Mg10 and Mg92- have higher energy barrier toward H2 dissociation; however, H2 dissociation over clusters that are two electrons shy from the closed electronic shell are relatively easier. As substrates, neither ZrO2(111) nor γ-Al2O3(100) affects the reactivity of the supported Ce2O4 toward CO2 adsorption and CO physisorption significantly; whereas the reactivity of Ce2O4 toward CO reactive adsorption were found to be affected by the two substrates very differently.
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Lynch, Charlotte Isabella. "First-principles calculations of NMR parameters for materials applications". Thesis, University of Oxford, 2017. https://ora.ox.ac.uk/objects/uuid:f44b9122-1826-410e-990d-a88dc3bb1432.
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Nuclear magnetic resonance (NMR) is a powerful experimental technique for probing the local environment of nuclei in materials. However, it can be difficult to separate the large number of interactions that are recorded in the resulting spectra. First-principles calculations based on quantum mechanics therefore provide much-needed support for interpreting experimental spectra. In this way, the underlying mechanisms recorded in experimental spectra can be investigated on an atomic level, and trends can be noted with which to guide the direction of future experiments. This thesis presents two cases in which first-principles calculations do just that. The first is an investigation of the perovskite structures of NaNbO3, KNbO3, LiNbO3 and the related solid solutions of NaxK1-xNbO3, KxNa1-xNbO3 and LixNa1-xNbO3 in order to study how structural disorder affects their NMR parameters. The second investigation involves the calculation of the Knight shift in platinum, palladium and rhodium---in their elemental bulk forms and in a set of surface structures. The Knight shift is a systematic shift in the NMR frequencies of metallic systems. It arises from the hyperfine interaction between the nuclear spins and the spins of the unpaired conduction electrons. When calculating the Knight shift, it is found that the Brillouin zone must be very finely sampled. A discussion of core polarisation is also presented. This is the polarisation of core electrons as a result of their interaction with valence electrons. In the case of Curie paramagnets, core polarisation can have a significant effect on the calculation of hyperfine parameters.
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Ullah, Habib. "First-principles density functional theory study of novel materials for solar energy conversion and environment applications". Thesis, University of Exeter, 2018. http://hdl.handle.net/10871/32949.
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To design an efficient solar energy conversion device, theoretical input is extremely important to provide the basic guideline for experimental scientists, to fabricate the most efficient, cheap, and stable device with less efforts. This desire can be made possible if computational scientist use a proper theoretical protocol, design an energy material, then the experimentalist will only invest weeks or months on the synthetic effort. This thesis highlights my recent efforts in this direction. Monoclinic BiVO4 is has been using as a photocatalyst due to its stability, cheap, easily synthesizable, narrow band gap and ideal VB (-6.80 eV vs vacuum) but inappropriate CB (-4.56 eV vs vacuum) edge position, responsible for its low efficiency. We have carried out a comprehensive experimental and periodic density functional theory (DFT) simulations of the pristine, Oxygen defective (Ov), Se doped monoclinic BiVO4 and heterojunction with Selenium (Se-BiVO4), to improve not only its CB edge position but photocatalytic and charge carrier properties. It is found that Ov (1% Oxygen vacancy) and mild doped BiVO4 (1 to 2% Se) are thermodynamically stable, have ideal band edges ~ -4.30 eV), band gaps (~1.96 eV), and small effective masses of electrons and holes. We have also investigated the contribution of Se to higher performance by effecting morphology, light absorption and charge transfer properties in heterojunction. Finally, it is found that Se makes a direct Z-scheme (band alignments) with BiVO4 where the photoexcited electron of BiVO4 recombine with the VB of Se, consequences electron-hole separation at Se and BiVO4, respectively, as a result, enhanced photocurrent is obtained. Theoretical study of β-TaON in the form of primitive unit cell, supercell and its N, Ta, and O terminated surfaces are carried out with the help of periodic DFT. Optical and electronic properties of all these different species are simulated, which predict TaON as the best candidate for photocatalytic water splitting contrast to their Ta2O5 and Ta3N5 counterparts. The calculated bandgap, valence band, and conduction band edge positions predict that β-TaON should be an efficient photoanodic material. The valence band is made up of N 2p orbitals with a minor contribution from O 2p, while the conduction band is made up of Ta 5d. Turning to thin films, the valence band maximum; VBM (−6.4 eV vs. vacuum) and the conduction band minimum; CBM (−3.3 eV vs. vacuum) of (010)-O terminated surface are respectively well below and above the redox potentials of water as required for photocatalysis. Charge carriers have smaller effective masses than in the (001)-N terminated film (VBM −5.8 and CBM −3.7 eV vs. vacuum). However, due to wide band gap (3.0 eV) of (010)-O terminated surface, it cannot absorb visible wavelengths. On the other hand, the (001)-N terminated TaON thin film has a smaller band gap in the visible region (2.1 eV) but the bands are not aligned to the redox potential of water. Possibly a mixed phase material would produce an efficient photoanode for solar water splitting, where one phase performs the oxidation and the other reduction. Computational study of an optically transparent, near-infrared-absorbing low energy gap conjugated polymer, donor−acceptor−donor (D-A-D) with promising attributes for photovoltaic application is reported herein. The D and A moiety on the polymeric backbone have been found to be responsible for tuning the band gap, optical gap, open circuit (Voc) and short-circuit current density (Jsc) in the polymers solar cells (PSC). Reduction in the band gap, high charge transformation, and enhanced visible light absorption in the D-A-D system is because of strong overlapping of molecular orbitals of D and A. In addition, the enhanced planarity and weak steric hindrance between adjacent units of D-A-D, resulted in red-shifting of its onset of absorption. Finally, PSC properties of the designed D-A-D was modeled in the bulk heterojunction solar cell, which gives theoretical Voc of about 1.02 eV. DFT study has been carried out to design a new All-Solid-State dye-sensitized solar cell (SDSC), by applying a donor-acceptor conjugated polymer instead of liquid electrolyte. The typical redox mediator (I1−/I3−) is replaced with a narrow band gap, hole transporting material (HTM). A unique “upstairs” like band energy diagram is created by packing N3 between HTM and TiO2. Our theoretical simulations prove that the proposed configuration will be highly efficient as the HOMO level of HTM is 1.19 eV above the HOMO of sanitizer (dye); providing an efficient pathway for charge transfer. High short-circuit current density and power conversion efficiency is promised from the strong overlapping of molecular orbitals of HTM and sensitizer. A low reorganization energy of 0.21 eV and exciton binding energy of 0.55 eV, confirm the high efficiency of HTM. Theoretical and experimental studies of a series of four porphyrin-furan dyads were designed and synthesized, having anchoring groups, either at meso-phenyl or pyrrole-β position of a zinc porphyrin based on donor–π–acceptor (D–π–A) approach. The porphyrin macrocycle acts as donor, furan hetero cycle acts as π-spacer and either cyanoacetic acid or malonic acid group acts as acceptor. Optical bandgap, natural bonding, and molecular bonding orbital (HOMO–LUMO) analysis confirm the high efficiency pyrrole-β substituted zinc porphyrins contrast to meso-phenyl dyads. DFT study of polypyrrole-TiO2 composites has been carried out to explore their optical, electronic and charge transfer properties for the development of an efficient photocatalyst. Titanium dioxide (Ti16O32) was interacted with a range of pyrrole (Py) oligomers to predict the optimum composition of nPy-TiO2 composite with suitable band structure for efficient photocatalytic properties. The study has revealed that Py-Ti16O32 composites have narrow band gap and better visible light absorption capability compared to individual constituents. A red-shifting in λmax, narrowing band gap, and strong intermolecular interaction energy (-41 to −72 kcal/mol) of nPy-Ti16O32 composites confirm the existence of strong covalent type interactions. Electron−hole transferring phenomena are simulated with natural bonding orbital analysis where Py oligomers found as donor and Ti16O32 as an acceptor in nPy-Ti16O32 composites. Sensitivity and selectivity of polypyrrole (PPy) towards NH3, CO2 and CO have been studied at DFT. PPy oligomers are used both, in the doped (PPy+) and neutral (PPy) form, for their sensing abilities to realize the best state for gas sensing. Interaction energies and amount of charges (NBO and Mulliken charge analysis) are simulated which reveal the sensing ability of PPy towards these gases. PPy, both in doped and neutral state, is more sensitive to NH3 compared to CO2 and CO. More interestingly, NH3 causes doping of PPy and de-doping of PPy+, providing evidence that PPy/PPy+ is an excellent sensor for NH3 gas. UV-vis and UV-vis-near-IR spectra of nPy, nPy+, and nPy/nPy+-X complexes demonstrate strong interaction of PPy/PPy+ with these atmospheric gases. The applications of graphene (GR) and its derivatives in the field of composite materials for solar energy conversion, energy storage, environment purification and biosensor applications have been reviewed. The vast coverage of advancements in environmental applications of GR-based materials for photocatalytic degradation of organic pollutants, gas sensing and removal of heavy metal ions is presented. Additionally, the presences of graphene composites in the bio-sensing field have been also discussed in this review.
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Cousland, Geoffrey. "Investigation of material properties of yttria-stabilised zirconia using experimental techniques and first-principles calculations". Thesis, The University of Sydney, 2014. http://hdl.handle.net/2123/12136.
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Zirconia (ZrO2) exists in a monoclinic phase at ambient temperature and pressure. Increasing the temperature of zirconia brings about a transition from the monoclinic to a tetragonal phase, and then the formation of a cubic phase. Yttria (Y2O3) can be added to zirconia in order to stabilise the high temperature phases, resulting in forms of tetragonal and cubic zirconia that are stable at ambient temperature. These materials are ceramics and are known collectively as yttria-stabilised zirconia (YSZ). The primary aim of this thesis is to investigate the structural, electronic, vibrational and mechanical properties of zirconia in its three ambient pressure polymorphs, together with YSZ for a range of yttria concentrations. Firstly, short-range order is investigated by medium energy x-ray photoemission spectroscopy for a YSZ sample with 8-9 mol % Y2O3, in combination with first-principles density-functional theory (DFT) calculations for two YSZ structural models with 10.35 mol % Y2O3 and shows that both structural models have short-range order that agrees with results from XPS experiments. Secondly, long-range order is analysed by comparing results of neutron scattering experiments for crystals of the same yttria concentration, with the same two YSZ models. Comparison with calculated vibrational density of states for the two structural models indicates the occurrence of long-range order for one of the structures in agreement with the experimental result. Thirdly, these calculations are extended to a full study of the electronic partial density of states and vibrational density of states for ZrO2, and for YSZ models with 10.35, 14, 17, 20 and 40 mol % Y2O3. Lastly, mechanical properties are investigated through first-principles calculations of the bulk modulus, shear modulus, Young's modulus and Poisson's ratio for the three ambient-pressure phases of ZrO2 and compared to existing available experimental results. The ideal strength of cubic ZrO2 is calculated for strains in the [100], [110] and [111] directions and for YSZ with concentrations of 6.67 mol % and 14.29 mol % Y2O3 for strains in the [100] and [110] directions. The ideal strength is also calculated for YSZ with concentration of 6.67 mol % Y2O3 co-doped with titanium, manganese, calcium or nickel.
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Zheng, Lixin. "Properties of Liquid Water and Solvated Ions Based on First Principles Calculations". Diss., Temple University Libraries, 2018. http://cdm16002.contentdm.oclc.org/cdm/ref/collection/p245801coll10/id/527565.
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PhysicsPh.D.
Water is of essential importance for life on earth, yet the physics concerning its various anomalous properties has not been fully illuminated. This thesis is dedicated to the understanding of liquid water from aspects of microscopic structures, dynamics, electronic structures, X-ray absorption spectra, and proton transfer mechanism. This thesis use the computational simulation techniques including density functional theory (DFT), ab initio molecular dynamics (AIMD), and theoretical models for X-ray absorption spectra (XAS) to investigate the dynamics and electronic structures of liquid water system. The topics investigated in this thesis include a comprehensive evaluation on the simulation of liquid water using the newly developed SCAN meta-GGA functional, a systematic modeling of the liquid-water XAS using advanced ab initio approaches, and an explanation for a long-puzzling question that why hydronium diffuses faster than hydroxide in liquid water. Overall, significant contributions have been made to the understanding of liquid water and ionic solutions in the microscopic level through the aid of ab initio computational modeling.
Temple University--Theses
Książki na temat "Density Functional Theory (DFT) - First Principles Calculations"
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Eriksson, Olle, Anders Bergman, Lars Bergqvist i Johan Hellsvik. Density Functional Theory. Oxford University Press, 2017. http://dx.doi.org/10.1093/oso/9780198788669.003.0001.
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Density functional theory (DFT) has established itself as a very capable platform for modelling from first principles electronic, optical, mechanical and structural properties of materials. Starting out from the Dirac equation for the many-body system of electrons and nuclei, an effective theory has been developed allowing for materials specific and parameter free simulations of non-magnetic and magnetic solid matter. In this Chapter an introduction will be given to DFT, the Hohenberg-Kohn theorems, the Kohn-Sham equation, and the formalism for how to deal with non-collinear magnetism.
Części książek na temat "Density Functional Theory (DFT) - First Principles Calculations"
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Sharma, Ramesh, Jisha Annie Abraham, Jagadish Chandra Mahato, Sajad Ahmed Dar i Vipul Srivastava. "Ferromagnetism in Mn and Fe Doped LuN: A Potential Candidate for Spintronic Application". W Density Functional Theory - Recent Advances, New Perspectives and Applications [Working Title]. IntechOpen, 2022. http://dx.doi.org/10.5772/intechopen.99774.
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Diluted magnetic semiconductor (DMS) materials have gained a lot of attention in the last decade due to their possible use in spintronics. In this chapter, the effect of transition metal (TM) i.e., Mn and Fe doping on the structural, electronic, magnetic as well as optical properties of pure and doped LuN has been presented from the first principles density functional theory (DFT) calculation with the Perdew-Burke-Ernzerhof-generalized gradient approximation (PBE-GGA) and Tran Blaha modified Becke-Johnson potential (TB-mBJ) as correlation potentials. The predicted Curie temperature is expected to be greater than room temperature in order to better understand the ferromagnetic phase stability, which has also been confirmed through the formation and cohesive energies. The calculated lattice constants for perfect LuN (rock-salt structure) are in good agreement with the experimental values. Interestingly, doping of Mn and Fe on pure LuN displays indirect band gap to a direct band gap with half metallic and metallic character. The detailed analyses combined with density of state calculations support the assignment that the Half-magnetism and magnetism are closely related to the impurity band at the origin of the hybridization of transition states in the Mn-doped LuN. Absorption spectra are blue shifted upon increase in dopant contents and absorption peaks are more pronounced in UV region. The refractive index and dielectric constant show increase in comparison to the pure LuN. According to the Penn’s model, the predicted band gaps and static actual dielectric constants vary. These band gaps are in the near visible and ultraviolet ranges, as well as the Lu0.75TM0.25N (TM = Fe, Mn) materials could be considered possible candidates for the production of optoelectronic, photonic, and spintronic devices in the future.
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Liu, S., I. Grinberg i A. M. Rappe. "Multiscale Simulations of Domains in Ferroelectrics". W Domain Walls, 311–39. Oxford University Press, 2020. http://dx.doi.org/10.1093/oso/9780198862499.003.0014.
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This chapter focuses on recent studies of ferroelectrics, where large-scale molecular dynamics (MD) simulations using first-principles-based force fields played a central role in revealing important physics inaccessible to direct density functional theory (DFT) calculations but critical for developing physically-based free energy functional for coarse-grained phase-field-type simulations. After reviewing typical atomistic potentials of ferroelectrics for MD simulations, the chapter describes a progressive theoretical framework that combines DFT, MD, and a mean-field theory. It then focuses on relaxor ferroelectrics. By examining the spatial and temporal polarization correlations in prototypical relaxor ferroelectrics with million-atom MD simulations and novel analysis techniques, this chapter shows that the widely accepted model of polar nanoregions embedded in a non-polar matrix is incorrect for Pb-based relaxors. Rather, the unusual properties of theses relaxor ferroelectrics stem from the presence of a multi-domain state with extremely small domain sizes (2–10 nanometers), giving rise to a greater flexibility for polarization rotations and the ultrahigh dielectric and piezoelectric responses. Finally, this chapter discusses the challenges and opportunities for multiscale simulations of ferroelectric materials.
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"Density functional theory (DFT) calculations for Raman spectroscopy". W Principles of Surface-Enhanced Raman Spectroscopy, 465–90. Elsevier, 2009. http://dx.doi.org/10.1016/b978-0-444-52779-0.00015-5.
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Wesolowski, Tomasz Adam, i Jacques Weber. "Applications of Density Functional Theory to Biological Systems". W Molecular Orbital Calculations for Biological Systems. Oxford University Press, 1998. http://dx.doi.org/10.1093/oso/9780195098730.003.0009.
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The term biological systems may be used in reference to a wide class of polyatomic systems. They can be defined as minimal functional units which perform specific biological functions: enzymatic reactions, transport across membranes, or photosynthesis. At present, such systems as a whole are not amenable to quantum-chemistry studies because of their large size. The smallest enzymes are built of few thousands of atoms (e.g., lysozyme consists of 129 amino-acid subunits), the smallest nucleic acids are of similar size (e.g., t-RNA molecules consist of about 80 nucleotide subunits), whereas biological membranes are even larger and include different biological macromolecules embedded in a phospholipide medium. On the other hand, a common-sense definition of the term biological systems refers to any chemical molecule or molecular complex which is involved in biological or biochemical processes. The latter definition, which will be used throughout this review, covers not only complete functional units performing biological functions but also fragments of such units. Theoretical studies have provided data on properties of such fragments and have helped understanding of the biological processes at the molecular level. Depending upon the size of such fragments, they can be studied by means of various quantum-chemical methods. Molecular systems of up to a few thousands of atoms can be studied using semi-empirical methods. For the Hartree-Fock or Kohn-Sham density functional theory (DFT) calculations, the current size limit is a few hundreds of atoms. (Throughout the text, Hartree-Fock refers to ab initio Self-Consistent Field calculations using the approximation of linear combination of atomic orbitals.) When the desired accuracy requires the calculation of electron correlation at the ab initio level, only systems containing no more than few tens of atoms can be treated. Therefore, a theoretician aiming at the elucidation of biological processes by quantum-mechanical calculations faces two crucial issues. The first one is the selection of a fragment for modeling at the quantum-mechanical level. The second one is the assessment of the effects associated with parts of the system which cannot be modeled at the quantum-mechanical level. In this review, the DFT studies of biological systems are divided into two groups corresponding to different ways of addressing the second aforementioned issue.
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Surendra Babu, Numbury. "Applications of Current Density Functional Theory (DFT) Methods in Polymer Solar Cells". W Density Functional Theory - Recent Advances, New Perspectives and Applications [Working Title]. IntechOpen, 2021. http://dx.doi.org/10.5772/intechopen.100136.
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DFT and time-dependant DFT (TD-DFT) quantum chemical calculations have become helpful for qualitative and quantitative analyses of materials at the molecular level. In this paper, we will attempt to outline successes and opportunities associated with the use of DFT and TD-DFT in OSC research. Density functional theory (DFT) has evolved as a QM method that is both rigorous and efficient enough to be employed in photovoltaic solar cell challenges in the last ten years. DFT is a prominent method for precisely and efficiently calculating molecular systems’ electrical and optical characteristics at a low computational cost. The possible uses of DFT to polymer solar cells were comprehensively examined in this article. First, the foundations of DFT are examined. Following that, the precision of DFT for studying photovoltaic properties particular to polymer solar cell design is highlighted. Next, this chapter looks at how DFT is used in polymer solar cell research and its accuracy. Following that, a discussion of how DFT works and how it can investigate polymer solar cell features will be given.
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Moriarty, John A. "Fundamental Principles in Metals Physics". W Theory and Application of Quantum-Based Interatomic Potentials in Metals and Alloys, 35–90. Oxford University PressOxford, 2023. http://dx.doi.org/10.1093/oso/9780198822172.003.0002.
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Abstract In this chapter, the underlying fundamental principles in metals physics necessary to develop quantum-based interatomic potentials in subsequent chapters are discussed. Density functional theory (DFT) is reviewed together with guidance from DFT electronic-structure calculations for both prototype simple metals and d-band transition metals. The nearly free electron (NFE) nature of the valence energy bands in simple metals allows a quantum treatment of the cohesive-energy functional within a plane wave basis set and the use of pseudopotential perturbation theory. The narrow d bands of transition series metals can be treated in a tight-binding (TB) representation with localized d basis states and simplified canonical d bands. The full hybrid NFE-TB nature of d-band metals, including sp-d hybridization, can be accommodated in a mixed basis set of plane waves and localized d states through the use of generalized pseudopotential theory, which is developed from a rigorous pseudo-Green’s function approach applied to DFT.
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Zaier, Rania, i Sahbi Ayachi. "Computational Study on Optoelectronic Properties of Donor-Acceptor Type Small π-Conjugated Molecules for Organic Light-Emitting Diodes (OLEDs) and Nonlinear Optical (NLO) Applications". W Density Functional Theory - Recent Advances, New Perspectives and Applications. IntechOpen, 2022. http://dx.doi.org/10.5772/intechopen.98590.
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Recently, donor-acceptor type molecule that contains electron-rich (D) and electron-deficient (A) moiety has emerged as an interesting approach of molecular design strategy to develop organic light-emitting diodes (OLEDs) and non-linear optical (NLO) devices. In this work, we report a theoretical investigation based on two donor-acceptor (D-A) type small π-conjugated molecules based on dithieno [3,2-b: 2′,3′-d] pyrrole (DTP) and anthracene derivatives. All of the theoretical calculations were performed by Density Functional Theory (DFT) approach at B3LYP/6-31 g(d) level of theory. The structural, electronic, optical and charge transfer properties were investigated. The effect of acceptor blocks (DPA and DTA) on the molecular characteristics was elucidated. The obtained results clearly show that the studied compounds exhibit non-coplanar structures with low electronic band gap values. These relevant structures exhibited important optical absorption and intense emission in the green-yellow region. NLO investigation based on static polarizability (α0), first-order hyperpolarizability (β0) and second-order hyperpolazabilty (ɣ0) demonstrated that the studied materials exhibit excellent NLO properties. Thus, the designed materials showed promising capabilities to be utilized in OLED and NLO applications.
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Íñiguez, J. "First-Principles Studies of Structural Domain Walls". W Domain Walls, 36–75. Oxford University Press, 2020. http://dx.doi.org/10.1093/oso/9780198862499.003.0003.
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This chapter discusses representative first-principles studies of structural domain walls in ferroics, focusing on the compounds that have received most attention by the simulations community so far: perovskite oxides. It describes in some detail a reduced number of case studies that come handy to illustrate different effects and to highlight the added value of the first-principles investigations. As regards the simulation methods, the chapter focuses on applications of density functional theory (DFT), typically employing an approximation for an effective treatment of ionic cores. A discussion on the application to domain-wall problems of first-principles-based methods for large-scale simulations of ferroelectrics and ferroelastics is also included. Finally, this chapter briefly on the opportunities and challenges for first-principles research in this field.
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Zurek, Eva, i Jochen Autschbach. "Density Functional Calculations of NMR Chemical Shifts in Carbon Nanotubes". W Computational Nanoscience, 279–306. The Royal Society of Chemistry, 2011. http://dx.doi.org/10.1039/bk9781849731331-00279.
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Computations of spectroscopic parameters of nanosystems can serve as an aid in experimental characterization. The focus of this article is on NMR (nuclear magnetic resonance) since in general this is one of the most versatile tools to study the structures, and properties of molecules and solids. After outlining the theory behind first–principles calculations of NMR parameters, it is illustrated that detailed information about the structure of carbon nanosystems can be obtained from these calculations. Theoretical studies of pristine SWNTs have indicated that 13C NMR may be used to determine the diameter distribution of a bulk sample. NICS (nucleus independent chemical shifts) have provided information about the aromaticity of various tubes, and the NMR chemical shifts of small molecules trapped in nanotubes have been calculated. Work on amine functionalized SWNTs has suggested that 13C NMR may be used to determine which nanotube carbons are derivatized, and perhaps even yield information about the diameter of the tubes. 13C NMR can potentially be useful to quantify the degree of fluorination. Theoretical studies on Stone-Wales defects have indicated that characteristic NMR signals may arise from atoms in the defect site. The tensor properties of nanotube NMR shielding is discussed.
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Moriarty, John A. "Introduction". W Theory and Application of Quantum-Based Interatomic Potentials in Metals and Alloys, 1–34. Oxford University PressOxford, 2023. http://dx.doi.org/10.1093/oso/9780198822172.003.0001.
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Abstract In this chapter, the concept of quantum-based interatomic potentials (QBIPs) is introduced as a viable means of extending the predictive power of density functional theory (DFT) quantum mechanics to the much longer length and time scales historically afforded only by simple empirical potentials. In metals and alloys, this extension of DFT is possible because the valence energy bands in these materials are amenable to simplified quantum treatments, leading to reliable expansion of the total energy in terms of weak interatomic matrix elements that define the potentials. In particular, QBIPs derived from first-principles generalized pseudopotential theory can power robust atomistic simulations on both simple- and transition-metal systems involving many millions of atoms. Because of their rigorous quantum origin, the physics content and accuracy of such QBIPs can also be systematically improved, aided by machine learning with state-of-the-art supercomputers where necessary.
Streszczenia konferencji na temat "Density Functional Theory (DFT) - First Principles Calculations"
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Mohlala, Lesego M., Rigardt A. M. Coetzee, Tien-Chien Jen i Peter A. Olubambi. "A First Principle Study on the Adhesion and Stability of Al203 (0001)/Pt (111) Film Interface". W ASME 2019 International Mechanical Engineering Congress and Exposition. American Society of Mechanical Engineers, 2019. http://dx.doi.org/10.1115/imece2019-10693.
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Abstract The first-principles calculation with density functional theory (DFT) is a powerful tool for studying solid-solid interfacial behaviour at the atomic scale. In this study, the interfacial properties of Al2O3 (0001)/Pt (111) atomic layer deposited film, such as adhesion strength, fracture toughness; interfacial energy and stability are investigated using the Cambridge Serial Total Energy Package (CASTEP) code in Material Studio. Two interface models with different Pt (111) configurations are investigated to elucidate their influence on the adhesion strength and interfacial stability. Moreover, the density of states plots (PDCS) is presented to further comprehend the electronic structures and bonding nature of interface. The work of adhesion obtained from the calculations is 2.836 J/m2 and 2.694 J/m2 for model 1 and 2 respectively. In addition, the interfacial energy for model 1 (−6.429J/m2) is smaller than that of model 2 (−5.881J/m2). The calculated results indicate that model 1 possesses high interface strength and thermodynamic stability. The lattice mismatch was calculated to be 10.46%, suggesting the formation of semi-coherent interface formation with coherent structural interface structures and misfit dislocation networks (MDN). The results obtained from the density functional theory simulations were compared and correlated with available literature.
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Sisto, A., X. Ruan, T. S. Fisher i J. B. Neaton. "Predicting the Properties of Nanostructured Metamaterials: Vertically Aligned Single-Walled Carbon Nanotube Arrays". W ASME 2011 International Mechanical Engineering Congress and Exposition. ASMEDC, 2011. http://dx.doi.org/10.1115/imece2011-64011.
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Recent advances in nanofabrication technology have facilitated the development of single-walled carbon nanotube (SWCNT) arrays with long-range order across macroscopic dimensions. However, an accurate generalized method of modeling these systems has yet to be realized. A multiscale computational approach combining first principles methods based on density functional theory (DFT) and extensions thereof to account for excited electron states, and classical electrodynamics simulations is described and applied to calculations of the optical properties of macroscopic SWCNT arrays. The first-principles approach includes the use of the GW and Bethe-Saltpeter methods, and the accuracy of these approximations is assessed through evaluation of the absorption spectra of individual SWCNTs. The fundamental mechanisms for the unique characteristics of extremely low reflectivity and high absorptance in the near IR are delineated. Furthermore, opportunities to tune the optical properties of the macroscopic array are explored.
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Balueva, Alla V., Ilia N. Dashevskiy, Patricia Todebush, Chasen Campbell i Eduardo Valdez. "First-Principle Calculations of the Binding Energy of the Coating Components of New Generation Dental Implants". W ASME 2019 International Mechanical Engineering Congress and Exposition. American Society of Mechanical Engineers, 2019. http://dx.doi.org/10.1115/imece2019-10059.
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Abstract We propose a new method of calculating adhesive strength of a novel bioactive nano-crystralline hydroxyapatite (HAp) coating of a dental implant by methods of Density Functional Theory (DFT) and Molecular Dynamics (MD) simulation. Hydroxyapatite is the material similar to the bone — that is why it is used in odontology to cover the implant to improve the process of osseointegration of the implant with the bone. It is also important to have a strong adhesive bond between the coating and the implant to avoid unpleasant situations dealing with the peeling of the coating. Our research focuses on understanding the strength of the bonds of interactions occurring during the process of spraying the dental implants, proposing factors that affect that strength, and ultimately looking at ways to improve the coating process. The goal of this work is to determine the strength of the interactions of the bio-nanocoating, hydroxyapatite, with titanium, which is the common material for the implant. Specifically the binding energy of different combinations of the constituents of the hydroxyapatite coating with titanium are calculated and ranked in order of intermolecular interactions. In the future, these components will be used to calculate the total binding energy of the HAp unit cell and the Ti (II) cation.
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Tao, Yi, Chenhan Liu, Juekuan Yang, Kedong Bi, Weiyu Chen i Yunfei Chen. "First Principles Study of Thermal Conductance Across Cu/Graphene/Cu Nanocomposition and the Effect of Hydrogenation". W ASME 2016 5th International Conference on Micro/Nanoscale Heat and Mass Transfer. American Society of Mechanical Engineers, 2016. http://dx.doi.org/10.1115/mnhmt2016-6318.
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In this work, the interfacial thermal conductance across Cu/graphene/Cu interfaces is investigated using the density functional theory (DFT) and the nonequilibrium Green’s function (NEGF) method. In order to study how hydrogenation of graphene affects thermal transport behaviors at the interfaces of Cu/graphene/Cu, we also analyze the interfacial thermal conductance across Cu/hydrogenated-graphene/Cu (Cu/H-graphene/Cu) with both double-sided and single-sided hydrogenated graphene. Our results show that, the interfacial thermal conductance across Cu/H-graphene/Cu interfaces is almost twice of the value across Cu/graphene/Cu interfaces. For Cu/H-graphene/Cu with double-sided hydrogenated graphene (Cu/DH-graphene/Cu), the hydrogen atoms between graphene and Cu layers provide additional thermal transport channels. While for Cu/H-graphene/Cu with single-sided hydrogenated graphene (Cu/SH-graphene/Cu), the hydrogen atoms not only provide additional thermal transport channels at the hydrogenated side of graphene, but also reduce the equilibrium separation between graphene and Cu layers at the non-hydrogenated side of graphene due to the transfer of massive electrons, which enhances the interface coupling between graphene and Cu layers. The phonon transmission shows that both double-sided and single-sided hydrogenation of graphene can increase the heat transport across the interface. Our calculation indicates that the interfacial thermal conductance of Cu/graphene/Cu nanocomposition can be improved by hydrogenation.
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Xing, Baihui, Jing Wang, Haotian Wei, Juan Shang, Zhengli Hua, Chaohua Gu i Jinyang Zheng. "Difference of Hydrogen Diffusion Regularity Between Interstice-Doped and Substitution-Doped Formed by Steel Carburizing". W ASME 2022 Pressure Vessels & Piping Conference. American Society of Mechanical Engineers, 2022. http://dx.doi.org/10.1115/pvp2022-84462.
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Abstract Carburizing treatment can improve the carbon content of the workpiece material, and obtain higher contact fatigue strength, bending fatigue strength, as well as higher surface hardness. After carburizing, the existence of carbon atoms can hinder the adsorption and diffusion of hydrogen, thus reducing the hydrogen embrittlement. First-principles plane wave calculations based on spin-polarized density-functional theory (DFT) and the generalized gradient approximation (GGA) have been used to study the adsorption and permeation of hydrogen on iron in the bulk with carbon interstice solid solution and carbon substitution solid solution. Considering that hydrogen diffusion is faster in martensitic tissue, bcc-Fe structure is selected for the model. The results show that the hydrogen diffusion rate Di in the interstice solid solution is higher than Ds in the substitution solid solution. The formation of substitution solid solution is promoted by more vacancies in the lattice. When the vacancy is occupied by carbon atoms, the hydrogen diffusion rate is reduced. This phenomenon is more obvious for Fe48C16 structure with higher carbon ratio. Besides, charge density diagram and state density analysis are also consistent with this conclusion. Therefore, during carburizing, Increasing the content of carbon and carbon substituted solid solution can reduce the penetration of hydrogen in the material.
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Bielawski, Mariusz, i Kuiying Chen. "Computational Evaluation of Adhesion and Mechanical Properties of Nanolayered Erosion-Resistant Coatings for Gas Turbines". W ASME Turbo Expo 2010: Power for Land, Sea, and Air. ASMEDC, 2010. http://dx.doi.org/10.1115/gt2010-22368.
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A computational method to evaluate fracture toughness of prospective erosion-resistant coatings using a combination of first-principles density functional theory (DFT) calculations and fracture mechanics is proposed. Elastic coefficients C11, C12 and C44, the ideal work of adhesion Wad, bulk moduls B, shear moduls G, and Young’s moduls E of transition metal nitrides with a cubic structure such as TiN, CrN, ZrN, VN and HfN are calculated. Both the G/B ratio and Cauchy pressure C12-C44 indicate brittle behaviour for TiN, ZrN and HfN and more metallic behaviour for CrN and VN. The fracture toughness KIC and interfacial fracture toughness KICInt for bi-layer combinations of these five nitrides is calculated along the [100] and [110] directions. The largest KIC value is obtained for HfN (2.14 MPa·m1/2) in (100) orientation and for TiN (2.16 MPa·m1/2) in (110) orientation. The lowest fracture toughness, in both orientations, is found for CrN. Among ten coherent interfaces of the five investigated nitrides the largest value of interfacial fracture toughness, KICInt = 3.24 MPa·m1/2, is recorded for the HfN/TiN interface in the (110) orientation.
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Kudo, Takuya, Qinqiang Zhang, Ken Suzuki i Hideo Miura. "First Principle Analysis of the Effect of Strain on Electronic Transport Properties of Dumbbell-Shape Graphene Nanoribbons". W ASME 2019 International Mechanical Engineering Congress and Exposition. American Society of Mechanical Engineers, 2019. http://dx.doi.org/10.1115/imece2019-11107.
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Abstract Graphene nanoribbons (GNRs), nano scale strips of graphene which consists of carbon hexagonal unit cell, are expected as next generation materials for high performance devices because of its unique super-conductive properties. When the strip width of graphene is cut into nano-scale, thinner than 70 nm, however, band gap starts to appear in the thin GNRs at room temperature, and thus, they show semiconductive properties. Previous studies have shown that the bad gap of GNR is highly sensitive to strain, which indicates that GNRs are candidates for a detective element of highly sensitive strain sensors. In practical applications, ohmic contact between a metallic electrode and a semiconductive detective element is indispensable for these sensors. By considering the effect of the width of GNRs on their electronic properties, dumbbell-shape GNRs (DS-GNRs) structures have been proposed for the basic structure of the GNR-base strain sensors, which consisted of GNRs with two different widths. Center portion of the DS-GNR is narrower than 70 nm and GNRs wider than 70 nm are attached at the both ends of the center GNR as electrode. Both semiconductive and metallic portions of a strain sensor consist of only carbon atoms using this DS-GNR structure. Even though this structure consists of one material, the effect of the interaction between two metallic and semiconductive GNRs must be clarified to realize the strain sensor with high performance. In this study, first principle calculations were applied to the analysis of the electronic band structure of the DS-GNR based on density functional theory (DFT). It was found that the local distribution of energy states of electrons and charges varied drastically as strong functions of the length of GNRs and the magnitude of the applied strain. The current through the DS-GNR structure was converged as the length of the semiconductive portion increased. In the models with enough length, transport property of the DS-GNR showed high sensitivity to strain. Thus, the effective resistivity of the structure varied from metallic to semiconductive, and therefore, this structure is appropriate for the next-generation highly sensitive and deformable strain sensors.
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Suzuki, Ken, Qinqiang Zhang i Xiangyu Qiao. "Effect of Tensile Strain on Electron Transport Properties of Dumbbell-Shape Graphene Nanoribbons With Metallic-Semiconducting Interfaces". W ASME 2021 International Mechanical Engineering Congress and Exposition. American Society of Mechanical Engineers, 2021. http://dx.doi.org/10.1115/imece2021-70930.
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Abstract In this study, first-principles calculations based on density functional theory (DFT) were performed to analyze in detail the electronic transport properties of dumbbell-shape graphene nanoribbons (DS-GNRs) and their strain dependence as a strong function of the combination of the basic structure of GNRs in the narrow segment and the structures at both ends of DS-GNRs. Then, the current-voltage characteristics (I-V characteristics) and orbital distributions of DS-GNRs were investigated to develop a highly sensitive DS-GNR-based strain sensor. By combining two GNRs with metallic and semiconducting electronic properties, a non-negligible transition layer (gradient Schottky barrier) was formed near the junction. The length of the transition layer was about five six-membered rings of carbon atoms. The formation of this transition layer is considered to be due to the exudation of the wave function from the wide segment to the narrow segment in DS-GNR. In the DS-GNR with metal-semiconductor interfaces, the strain dependence of the electronic transport properties was very complicated due to the presence of the transient Schottky barrier. On the other hand, in a DS-GNR consisting of two metallic GNRs, the Schottky barrier and the transition layer disappeared, and stable current-voltage and piezoresistive characteristics close to those of a single GNR were observed. The predicted gauge factor of DS-GNRs was larger than that of conventional metal foils (gauge factor 2–5) and close to that of conventional polysilicon (gauge factor ±30). These results indicate that DS-GNRs have the potential to produce highly sensitive and reliable strain sensors.
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Payne, M. C. "The role of first principles calculations in materials modelling". W Density functional theory and its application to materials. AIP, 2001. http://dx.doi.org/10.1063/1.1390180.
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Kitawaki, Yohei, i Hiroshi Yamagami. "First-Principles Calculations of Orbital Polarization in Relativistic Density Functional Theory". W Proceedings of the 29th International Conference on Low Temperature Physics (LT29). Journal of the Physical Society of Japan, 2023. http://dx.doi.org/10.7566/jpscp.38.011170.
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