Dissertations / Theses: 'Ab initio calculations'

1

Li, Sa. "Materials Design from ab initio Calculations." Doctoral thesis, Uppsala : Acta Universitatis Upsaliensis : Univ.-bibl. [distributör], 2004. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-4274.

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2

黃新祥 and Sun-cheung Wong. "Ab initio calculations of silicon clusters." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 1998. http://hub.hku.hk/bib/B3122197X.

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3

Tam, Mary Christina. "Ab initio Calculations of Optical Rotation." Diss., Virginia Tech, 2006. http://hdl.handle.net/10919/27214.

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Coupled cluster (CC) and density functional theory (DFT) are highly regarded as robust quantum chemical methods for accurately predicting a wide variety of properties, such as molecular structures, thermochemical data, vibrational spectra, etc., but there has been little focus on the theoretical prediction of optical rotation. This property, also referred to as circular birefringence, is inherent to all chiral molecules and occurs because such samples exhibit different refractive indices for left- and right- circularly polarized light. This thesis focuses on the theoretical prediction of this chiroptic property using CC and DFT quantum chemical models. Several small chiral systems have been studied, including (S)-methyloxirane, (R)-epichlorohydrin, (R)-methylthiirane, and the conformationally flexible molecules, (R)-3-chloro-1-butene and (R)-2-chlorobutane. All predicted results have been compared to recently published gas-phase cavity ringdown polarimetry data. When applicable, well-converged Gibbs free energy differences among confomers were determined using complete-basis-set extrapolations of CC energies in order to obtain Boltzmann-averaged specific rotations. The overall results indicate that the theoretical rotation is highly dependent on the choice of optimized geometry and basis set (diffuse functions are shown to be extremely important), and that there is a large difference between the CC and DFT predicted values, with DFT usually predicting magnitudes that are larger than those of coupled cluster theory.
Ph. D.

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4

Wong, Sun-cheung. "Ab initio calculations of silicon clusters." Hong Kong : University of Hong Kong, 1998. http://sunzi.lib.hku.hk/hkuto/record.jsp?B20192708.

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Nazé, Cédric. "Relativistic ab initio calculations of isotope shifts." Doctoral thesis, Universite Libre de Bruxelles, 2012. http://hdl.handle.net/2013/ULB-DIPOT:oai:dipot.ulb.ac.be:2013/209637.

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Quand les effets de la masse finie du noyau et de la distribution de charge spatiale sont pris en compte dans l’Hamiltonien décrivant un système atomique, les isotopes d’un élément, caractérisés par le même nombre de protons mais un nombre différent de neutrons, ont des niveaux d’énergie électronique différents. Le déplacement entre les niveaux d’énergie (pour un même état quantique) de deux isotopes différents est appelé le déplacement isotopique de niveau. De manière générale, on peut distinguer les déplacements isotopiques de champ (field shift) et les déplacements isotopiques de masse (mass shift). Pour les systèmes à plus d’un électron, le specific mass shift (SMS) apparaît. Grâce à sa faible pondération, le paramètre SMS peut être traité comme une perturbation de l’Hamiltonien ;son estimation fait appel aux intégrales de Vinti [5].

Dans un contexte relativiste, les programmes grasp2K [2] et mcdf-gme [1] permettent de résoudre les équations de Dirac-Fock associées à un état multiconfigurationnel et d’en fournir l’énergie ainsi que la représentation numérique des orbitales monoélectroniques. Nous avons créé et introduit dans le programme mcdf-gme une sous-routine capable d’estimer les paramètres de masse et de champ à partir des fonctions d’onde multiconfigurationnelles. Pour le programme GRASP2K, un module indépendant à été créé.

Par ailleurs, un opérateur plus complet impliquant des corrections en αZ, a été dérivé par Shabaev [4] et, de manière indépendante, par Palmer [3]. Nous avons déduit la forme tensorielle de cet opérateur et avons également implémenté dans les programmes cités ci-dessus le calcul de ses éléments de matrice.

Grâce à ces outils nous avons pu étudier la détérioration de l’opérateur d’énergie cinétique pour estimer le normal mass shift et travailler divers systèmes comme le lithium neutre et sa séquence isoélectronique. Par la suite nous avons également travaillé sur les séquences isoélectroniques du bore, du béryllium, du carbone et de l’azote. Enfin, certains effets isotopiques ont été étudiés pour plusieurs transitions dans le baryum neutre.

Bibliographie

[1] J. P. Desclaux. A relativistic multiconfiguration Dirac-Fock package. In E. Clementi, editor, Methods and Techniques in Computational Chemistry - vol. A :Small Systems of METTEC, page 253. STEF, Cagliari, 1993.

[2] P. Jönsson, X. He, C. Froese Fischer and I. P. Grant. The GRASP2K relativistic atomic structure package. Comput. Phys. Commun. 177 :597–622, 2007.

[3] C. W. P. Palmer. Reformulation of the theory of the mass shift. J. Phys. B :At. Mol. Phys. 20 :5987–5996, 1987.

[4] V. M. Shabaev and A. N. Artemyev. Relativistic nuclear recoil corrections to the energy levels of multicharged ions. J. Phys. B :At. Mol. Phys. 27 :1307–1314, 1994.

[5] J. P. Vinti. Isotope shift in magnesium. Phys. Rev. 56 :1120–1132, 1939.
Doctorat en Sciences de l'ingénieur
info:eu-repo/semantics/nonPublished

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Ernst, Margot Christiana. "Ab initio calculations on chiral cobalt (III) complexes." Diss., Georgia Institute of Technology, 1992. http://hdl.handle.net/1853/27429.

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7

區逸賢 and Yat-yin Au. "Ab initio calculations: an extension of Sankey's method." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 1999. http://hub.hku.hk/bib/B31222195.

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8

Comeau, Donald Clifford. "Large-scale ab initio molecular electronic structure calculations /." The Ohio State University, 1990. http://rave.ohiolink.edu/etdc/view?acc_num=osu1487684245466345.

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9

Au, Yat-yin. "Ab initio calculations : an extension of Sankey's method /." Hong Kong : University of Hong Kong, 1999. http://sunzi.lib.hku.hk/hkuto/record.jsp?B21482706.

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10

Marzari, Nicola. "Ab-initio molecular dynamics for metallic systems." Thesis, University of Cambridge, 1996. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.285270.

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11

Chang, Jianlin. "Ab initio calculations of semiconductor surfaces and molecular clusters." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1997. http://www.collectionscanada.ca/obj/s4/f2/dsk3/ftp05/nq22449.pdf.

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12

Haynes, P. "Linear-scaling methods in ab initio quantum-mechanical calculations." Thesis, University of Cambridge, 1998. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.603888.

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The work described in this dissertation concerns the development of new methods for performing computer simulations of real materials from first principles or ab initio i.e. using the fundamental equations of quantum mechanics and only well-controlled approximations. In particular, these methods have been developed within the framework of density-functional theory and therefore lie in the realms of both quantum chemistry and computational condensed matter physics. The work is particularly concerned with methods which are efficient in the sense that the computational effort required scales only linearly with system-size (i.e. the volume or number of electrons) whereas traditional methods have scaled with the cube of the system-size which has restricted their range of applicability. The aim of this work is therefore to extend the scope of ab initio quantum-mechanical calculations beyond what is currently possible. Density-functional theory has traditionally been applied by making use of a mapping from the system of interacting electrons to a fictitious system of non-interacting particles. However, the need to maintain the mutual orthogonality of the wave functions of the fictitious system leads to the cubic scaling mentioned above, and is ultimately responsible for limiting the maximum size of systems which can be treated. Making use of a reformulation of the problem in terms of the single-particle density-matrix eliminates the need to work with the wave functions directly. Moreover, exploiting the short-ranged nature of the density-matrix leads in principle to a linear-scaling method. The dissertation tackles two issues which are relevant to obtaining practical schemes for performing linear-scaling calculations. Firstly a localised basis set is developed which is used to describe the density-matrix computationally. Analytic results for several key quantities required by the calculation are derived, namely the overlap, kinetic energy and non-local pseudopotential matrix elements. These results allow accurate calculation of the total energy of the system and have been implemented and tested computationally. Secondly, the dissertation discusses several methods for imposing the difficult non-linear idempotency constraint on the density-matrix.

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Sitch, Paul Kirst. "Ab-initio calculations of dislocation related properties in semiconductors." Thesis, University of Exeter, 1994. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.240399.

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14

Pinheiro, JosÃ Auri. "crystals of glutamic acid: growth, characterization and calculations ab initio." Universidade Federal do CearÃ, 2006. http://www.teses.ufc.br/tde_busca/arquivo.php?codArquivo=7576.

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nÃo hÃ
O trabalho realizado nesta tese visa a cristalizaÃÃo do Ãcido glutÃmico, favorecendo a obtenÃÃo da fase α (metaestÃvel) em relaÃÃo ao polimorfo β. ApÃs a obtenÃÃo dos cristais realizaram-se as medidas experimentais de fluorescÃncia, com vistas a comparaÃÃo com os dados teÃricos obtidos, considerando as limitaÃÃes do mÃtodo de simulaÃÃo ab-initio utilizado. Os cÃlculos de primeiros princÃpios foram realizados para estudar as propriedades do cristal do Ãcido glutÃmico nas modificaÃÃes α e β no que se refere ao aspecto estrutural, eletrÃnico (estrutura de bandas) e Ãptico (funÃÃo do complexo dielÃtrico), tudo isto em relaÃÃo ao polimorfismo conformacional. A teoria do funcional da densidade (TFD) Ã considerada usando uma base de ondas planas, pseudopotenciais ultramacios, e o potencial de correlaÃÃo-troca dentro do Generalized-Gradient Approximation (GGA). Os parÃmetros de rede estÃo de acordo com os resultados experimentais, embora na forma α Ã previsto ter um gap indireto entre os pontos de alta simetria  e X, igual a 4.69 eV, para a forma β nÃo pode-se tirar uma conclusÃo sobre o gap direto (-), devido a imprecisÃo do cÃlculo. A funÃÃo dielÃtrica de ambos os polimorfos sÃo muito semelhantes no caso de uma amostra policristalina, mas difere fortemente no caso da polarizaÃÃo da luz das faces do cristal 100 e 010.
Done the work accomplish in this thesis it seeks the crystallization of the glutamic acid, favoring the obtaining of the phase α (metastable) in relation to the polymorph β. After the obtaining of the crystals they did take place the experimental measures of fluorescence, with views the comparison with the obtained theoretical data, considering the limitations of the method of simulation used ab-initio. Were the calculations of first principles accomplished to study the properties of the crystal of the glutamic acid in the modifications α and β in what she refers to the aspect structural, electronic (structure of bands) and optical (function of the dieletric complex), everything this in relation to the polymorphism conformational. The theory of the functional of the density (TFD) is it considered using a base of plane waves, pseudo potential ultrasoft, and the correlation-change potential inside of the Generalized-Gradient Approximation (GGA). Are the net parameters in agreement with the experimental results, although in the form α is it foreseen to have an indirect gap between the points of high symmetry and X, equal to 4.69 eV, for the form β a conclusion cannot be reached on the direct gap (-), due to imprecision of the calculation. The function dieletric of both polymorph are very similar in the case of a sample polycrystal, but it differs strongly in the case of the polarization of the light of the faces of the crystal 100 and 010

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15

Persson, Kristin Aslaug. "Thermodynamical and Dynamical Instabilities from Ab initio Electronic-Structure Calculations." Doctoral thesis, KTH, Physics, 2001. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-3137.

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16

Persson, Kristin. "Thermodynamical and dynamical instabilities from Ab initio electronic-structure calculations /." Stockholm : Tekniska högsk, 2001. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-3137.

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17

Major, Zsuzsanna. "The electronic structure of weak ferromagnets and ab initio calculations." Thesis, University of Bristol, 2004. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.409003.

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18

Aas, C. J. "Ab initio calculations of the magnetic properties of bimetallic alloys." Thesis, University of York, 2013. http://etheses.whiterose.ac.uk/4302/.

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Magnetic recording technology is ubiquitous in the modern world and constitutes a corner stone of current research and development. Recent inventions such as heat-assisted magnetic recording and exchange-coupled media has focused magnetic recording research towards alloys exhibiting strong magnetocrystalline anisotropies. In this thesis, we investigate, from first principles using the screened Korringa-Kohn-Rostoker method, the effect of a range of compositional and microstructural defects and features upon the magnetocrystalline anisotropy energy (MAE) of FePt and CoPt alloys. We show that localised Pt alloying affects the MAE of bulk Co primarily through the Pt-induced effects on the Co sites. We demonstrate that stacking faults often reduce the Co MAE and that the effect of composite stacking faults upon the MAE is not necessarily additive, but synergistic. By varying the unit cell geometry and the compositional parameters of FePt, we show that the formation of complete Fe layers is, generally, the dominant factor in maintaining a large MAE. We investigate the magnetic properties (spin moments, magnetocrystalline anisotropy and magnetic exchange) across an Fe/FePt/Fe multi-layer and show that the effective exchange exhibits a strong reduction at the Fe/FePt interfaces and that the MAE of the whole multilayer system is very slightly reduced by the presence of the Fe/FePt interfaces. Across all systems, we observe that localised features such as stacking faults, interfaces and localised alloying incur relatively long-ranged spatial oscillations in the MAE, which may, in turn, cause significant finite-size effects on the nano-scale.

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19

Hooper, Nicole. "Some studies of small reactive intermediates with ultraviolet photoelectron spectroscopy." Thesis, University of Southampton, 2002. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.252045.

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Fikar, Ondřej. "Ab initio výpočty křivek rozpustnosti tuhých roztoků." Master's thesis, Vysoké učení technické v Brně. Fakulta strojního inženýrství, 2019. http://www.nusl.cz/ntk/nusl-400461.

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This diploma thesis is focused on a theoretical study of the phase stability of solid solutions in selected aluminium and silver alloys. The ab initio calculations were performed using projected augmented waves method and the thermal dependencies of thermodynamic quantities were acquired using phonon calculations. The main focus of this work is the of aluminium-germanium alloy, while the other examined alloys (Al-Pb, Ag-Ge and Ag-Pb) serve the purpose of comparison of the solid solubility prediction and its reliability in systems with different composition. The temperatures, at which the solid solutions become stable, were evaluated using the energy difference between possible states and this evaluation was carried out for different contributions to the total energy. Also the electronic and phonon densities of states were calculated for all pure elements and solid solutions. The temperatures of solubility were compared to the experimental ones provided by the CALPHAD method and the individual contributions to the total energy were determined and depicted. The results obtained in this work tend to underestimate temperatures of solubility of individual solid solutions by hundreds of Kelvin.

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21

Chauvin, Sophie. "Cobaltates in the high-doping regime : Insights from first-principles calculations and extended dynamical mean-field theory." Thesis, Université Paris-Saclay (ComUE), 2016. http://www.theses.fr/2016SACLX110/document.

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Comme de nombreux autres oxydes de métaux de transition lamellaires, les cobaltates dopés au sodium, NaxCoO2, présentent un riche diagramme de phase. Les nombreuses instabilités (magnétiques, de charge) qui les caractérisent seraient notamment le fruit des corrélations électroniques. Dans cette thèse, nous nous intéressons au cas fortement dopé x=2/3 (proche de la limite de l'isolant de bande). Expérimentalement, ce composé est sujet à une disproportion de charge locale sur les atomes de cobalt, ce qui en fait un terrain d'étude privilégié pour le calcul des fonctions de corrélation de charge. Le traitement théorique de ce système est difficile a bien des égards. D'abord, la corrélation électronique demande de recourir à des approximations avancées. Ensuite, le système est sensible aux détails microscopiques, tels que transcrits dans la structure électronique réelle. Dans cette thèse, nous abordons ces deux aspects, à travers un approche sur modèle et une approche ab initio.Nous examinons d'abord l'effet des corrélations au niveau d'un modèle sur réseau triangulaire, pertinent pour les cobaltates. La compétition entre les interactions de Coulomb locale et non-locale sur un modèle de Hubbard étendu donne lieu à des fluctuations de charge, que nous traitons grâce à la théorie du champ moyen dynamique étendue. Nous dressons le diagramme de phase de notre modèle en fonction des interactions locales et non-locales. Celui-ci présente une transition du second ordre entre un état métallique homogène et une phase ordonnée de charge. Nous calculons les observables à une et deux particules dans la phase homogène, et nous déterminons l'effet des corrélations sur ces deux types d'observables. Nous interprétons ces résultats comme des conséquences du fort dopage. Nous identifions une région du diagramme de phase où la partie statique de l'interaction de Coulomb écrantée devient négative. Enfin, nous montrons comment incorporer un terme de Fock non-local à ces calculs, et nous détaillons son effet sur le diagramme de phase et sur les observables physiques.En complément de notre approche sur modèle, nous étudions les détails microscopiques du matériau réel grâce à la théorie de la fonctionnelle de la densité. Nous analysons le rôle de l'hybridation avec l’oxygène et des processus de saut électronique sur la structure de bandes pour les plans de cobalt-oxygène. Nous clarifions l'effet de certains paramètres physiques, tels que le dopage au sodium, l'arrangement cristallin ou le magnétisme, sur la structure électronique. Puis nous calculons la susceptibilité de charge selon les premiers principes, selon des approximations suggérées par notre étude de modèle sur réseau.La comparaison entre les calculs sur modèle et ab initio montre que ces approches se complètent l'une l'autre. D'une part, le modèle permet de dégager les approximations pertinentes pour le calcul des fonctions de corrélation de charge. D'autre part, les calculs ab initio et la compréhension des processus microscopiques sont le préalable à la construction d'un modèle réaliste et prédictif
As many other layered transition-metal oxides, sodium-doped cobaltates, NaxCoO2, present a rich phase diagram. They display numerous instabilities (magnetic, charge-order), originating most likely from electronic correlations. In this thesis, we focus on the case x=2/3, in the strong-doping limit (close to the band-insulating limit). An experimentally-observed charge disproportionation on the cobalt atoms makes this particular composition an interesting playground to study charge-correlation functions. The theoretical treatment of this system is difficult in several aspects. In order to capture electronic correlations, one needs to resort to advanced non-perturbative approaches. Also, the system is sensitive to its microscopic details, as encoded in the real electronic structure. This is why, in this thesis, we adopt model as well as ab initio approaches to address both these issues.We first study the effect of correlations at the model level, on a triangular lattice, specifically designed for the cobaltates. The interplay between local and non-local Coulomb interactions gives rise to charge fluctuations, which we capture using the Extended Dynamical Mean-Field Theory. We establish the phase diagram of our model as a function of local and non-local interactions. It displays a second-order phase transition between a homogeneous metallic phase, and a charge-ordered phase. We compute one and two-particle observables in the homogeneous phase, and we analyse how they are influenced by correlations. We show that our findings can be understood as a consequence of the strong doping. We find a region of the phase diagram where the static screened Coulomb interaction becomes negative. Finally, we show how to incorporate a non-local Fock term in the calculation of the self-energy, and how it influences the phase diagram and the physical observables.Next, in order to complement the model approach, we study the microscopic details of the real sodium-cobaltates by using Density-Functional Theory. We analyse the effect of oxygen hybridisation and electronic hopping processes on the band structure of cobalt-oxygen planes. We study the effects of sodium doping, crystal structure and magnetism, on the band structure of this material. Then, we compute the charge susceptibility from first principles in the independent-particle approximation and in the random-phase approximation. We use the insight gained from the model calculation to discuss these results.The comparison between the model and the ab initio calculations shows that these approaches are complementary. The model enables us to define the best approximations for the calculation of charge correlation functions. The ab initio calculations, and the detailed understanding of microscopic electronic processes are the prerequisite for a model that is both realistic and predictive

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Berghold, Gerd. "Towards very large scale DFT electronic structure calculations." [S.l. : s.n.], 2001. http://www.bsz-bw.de/cgi-bin/xvms.cgi?SWB9519379.

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Liu, Limin. "Ab initio calculations on HX2-Systems (X=F, C1, Br, I)." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 2000. http://www.collectionscanada.ca/obj/s4/f2/dsk1/tape3/PQDD_0017/MQ54722.pdf.

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Sun, Weiwei. "Heavy Metal Compounds and Hydrogen Storage Materials from Ab Initio Calculations." Licentiate thesis, KTH, Tillämpad materialfysik, 2013. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-120062.

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In principle, most of the properties of solids can be determined by their electronic structures. So the understanding of electronic structures is essential. This thesis presents two classes of materials using ab initio method based on density functional theory. One is heavy metal compounds like Ta2AlC, ThO and the other one is hydrogen storage material namely MgH2 surfaces. The study of correlation and relativistic effects in Ta2AlC are presented. Based on our results, Ta2AlC is a weakly correlated system. Our study shows that the spin - orbital coupling does not play a very important role where as the other relativistic corrections such as mass velocity and Darwin terms have a significant effect on the electronic properties. The stability of rock salt like ThO has been proposed based on the first principle calculation. ThO can be stabilized under pressure. The driving force is the sd to f charge transfer in Th. We have investigated the energetics of hydrogen desorption from the MgH2 (110) and (001) surfaces. The doping of foreign metal elements and strain were used to reduce the dehydrogenation energy. The reduction in dehydrogenation energy is caused by the charge localization on the metal atoms which leads to destabilization and the weakening of metal - hydrogen bonds.

QC 20130327

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Nelson, Alistair David. "Ab initio calculations on the ground and excited states of molecules." Thesis, University of Edinburgh, 2002. http://hdl.handle.net/1842/15497.

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This Thesis contains the results obtained using correlated ab initio calculations for both the ground and excited states of a series of triatomic molecules, such as ozone (O₃) and the halogen oxides (X₂O, where X = F, CI, Br and I), together with a subset of the pseudo halogens, including fluorine, chlorine, bromine and iodine azide, isocyanate and isothiocyanate. Chapter 1 presents a summary of the methods used to carry out these calculations, starting with the Schrödinger equation and the methods used to solve it, and proceeding to the discussion of differing methodologies such as SCF, multi-configuration SCF and CASSCF, CI and MP2 methods. Chapter 2 describes some of the ground state properties calculated in this work, in quantum chemical terminology, as well as discussing some of the differences in values obtained by experimental and theoretical methods. Chapters 3 and 4 are concerned with the studies on the ozone molecule, with the former covering the ground state and its properties, and the latter presenting the results for the excited states. Chapter 4 includes a comparison with the experimental UV and VUV spectra in the 0 to 12eV region, and assignments are offered for the valence and Rydberg states found in this energy range. These results suggest that the number of states presently identified by spectroscopic means are well short of those that might be expected in the energy range. Chapters 5 describes the study of a subset of the pseudo halogens. These results are concerned solely with the ground state and molecular properties relating to the wave-function as well as structural and ground state spectra such as infrared spectra; where possible these calculated results have been compared with experimental data. The final two Chapter 6 and 7, are devoted to the X₂O molecules, where X = F, Cl, Br and I. Chapter 6 discusses the ground state properties of the molecules and compares with experiment where such data is known, and predicts the structure and properties of I₂O. The final Chapter covers the excited states of the X₂O molecules, where just the cases where X = F, Cl and Br are examined. Theoretical UV+VUV spectra produced, for each molecule, and Cl₂O has been compared with the experimental data.

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Ballard, Charles Conor. "Ab initio calculations on the ground and excited states of molecules." Thesis, University of Edinburgh, 1993. http://hdl.handle.net/1842/14836.

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In this work the results of highly correlated ab initio calculations on the low-lying states of propyne, furan, and the copper dimer are reported. The excitation energies obtained are used to interpret the electronic spectra of these molecules. The electronic spectra of propyne and furan have been studied using multi-reference configuration interaction techniques. For both molecules the calculations comprise the low-lying valence and s, p, and d Rydberg states, all calculations being performed at the SCF optimised geometry. A variety of basis sets were used; the inclusion of diffuse polarisation functions in the basis set is found to improve the description of the excitation processes. In contrast, the use of polarisation functions optimised for the molecular ground state has negligible effect. The electronic spectrum of propyne is interpreted on the basis of these results to be similar to that of acetylene. The computed excitation energies for the valence states of furan differ drastically from earlier theoretical results. The present results are compared to new experimental data and found to give a consistent picture for the low-lying states. The configuration interaction procedure was also utilised to determine the excitation energies of the ungerade states of Cu₂ arising from the ²S+ ²D asymptote. Much of the work took the form of a preliminary investigation to investigate the feasibility of the technique and applicability of a variety of basis sets. The calculations were performed at 2.20 AA, arbitrarily, chosen to be close to the experimental equilibrium geometry. The inclusion of f-functions was found to be important in describing excitations involving states with different numbers of d electrons. Large reorganisation effects are found to accompany these excitations, which are not adequately described at the CISD level.

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Rivas, Gildardo. "Ab initio calculations of optical constants from UV to X-rays /." Thesis, Connect to this title online; UW restricted, 2004. http://hdl.handle.net/1773/9629.

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Dawson, William G. "Ab initio LCAO electronic structure calculations of layered transition-metal compounds." Thesis, University of Bath, 1988. https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.380362.

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29

Rich, Brian. "Ab Initio Quantum Chemistry Calculations of Phosphorous Oxide Caged Cluster Compounds." Digital Commons @ East Tennessee State University, 2013. https://dc.etsu.edu/honors/174.

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The objective of my thesis was to add to a catalogue of molecular structures that is being compiled as a part of the Standoff Detection Project. The optimized geometry of P8O20 and P20O20 were calculated using restricted Hartree-Fock Theory, using the standard quantum mechanics and computational chemistry programs ECCÈ and NWChem. Unfortunately, due to the extremely time consuming nature of these calculations there was not enough time to complete the calculations for P24O48 and P24O60.

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Asiri, Yazeed. "Ab Initio and Semi-Empirical Calculations of Cyanoligated Rhodium Dimer Complexs." Digital Commons @ East Tennessee State University, 2017. https://dc.etsu.edu/etd/3177.

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Molecular modeling, using both ab initio and semi-empirical methods has been undertaken for a series of dirhodium complexes in order to improve the understanding of the nature of the chemical bonding in this class of homogeneous catalysts. These complexes, with carboxylamidate and carboxylate ligands, are extremely functional metal catalysts used in the synthesis of pharmaceuticals and agrochemicals. The X-ray crystallography shows anomalies in the bond angles that have potential impact on understanding the catalysis. To resolve these issues, minimum energy structures of several examples (e.g. Rh2(NHCOCH3)4, Rh2(NHCOCH3)4NC, Rh2(CO2CH3)4, Rh2(CO2CH3)4NC, Rh2(CHO2)4, and Rh2(CHO2)4NC) were calculated using Hatree-Fock and Density Functional Theory/B3LYP with the LANL2DZ ECP (Rh), and cc-pVDZ (all other atoms) basis sets.

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Kováčik, Roman. "Characterization of catalyst surfaces by ab-initio thermodynamics and STM data calculations." [S.l.] : [s.n.], 2007. http://deposit.ddb.de/cgi-bin/dokserv?idn=98518468X.

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De, Gortari Itzam. "Ab initio calculations of NMR chemical shifts for structure determination in biology." Thesis, University of Cambridge, 2006. https://www.repository.cam.ac.uk/handle/1810/265479.

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In this thesis we present an application of a computational method for calculating nuclear Magnetic Resonance chemical shifts to structure determination in Biology. We investigate and summarise the most important structural contributions to the chemical shift. Even though the NMR chemical shift has direct relation to the global structure it is shown that there are two main dominant contributions: I3C-a depends mainly on the secondary structure and 15-N NMR chemical shift depends mainly on hydrogen bonds. The importance of other relevant contributions to the chemical shifts, such as solvent and dynamical effects, is demonstrated by testing our computational method on proteins and by comparing theory and experiment. The thermal effects on the chemical shift in the solid are studied by combinig ab initio molecular dynamics simulations and NMR chemical shift calculations. Other factors affecting the chemical shift are investigated by constructing ideal models from which we can extract information about the nature of the hydrogen bonds in helical structures. By doing these calculations we suggest specific experimental measurements of chemical shift which could differentiate structures that have minor structural variations between them, eg. the three different types of helices in proteins. The last topic studied in this thesis, namely amyloid fibrils, is presented as a starting point for future work.

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Singh, David. "AB initio calculations of the properties of indium antimonide and indium arsenide." Thesis, University of Ottawa (Canada), 1985. http://hdl.handle.net/10393/5016.

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Rolke, James M. "Orbital electron density from electron momentum spectroscopy : comparison with AB initio calculations." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1997. http://www.collectionscanada.ca/obj/s4/f2/dsk3/ftp04/nq25146.pdf.

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Beveridge, Allan John. "Ab initio calculations of organic molecules : substituted ethylenes, azoles and merocyanine dyes." Thesis, University of Edinburgh, 1985. http://hdl.handle.net/1842/10797.

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Casanova, Páez Marcos Andrés. "Study of isolated point charge defects in CdTe by Ab-Initio calculations." Tesis, Universidad de Chile, 2017. http://repositorio.uchile.cl/handle/2250/145765.

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Magíster en Ciencias, Mención Física
La generación de energía a través de la radiación solar es una de las tecnologías más prometedoras para un futuro sustentable. En particular, las tecnologías fotovoltaicas de telururo de cadmio (CdTe) aún se encuentran lejos de llegar a su maxima eficiencia, pero aín así han logrado competir en precio respecto de las tradicionales celdas fotovoltaicas a base de silicio cristalino. En las celdas fotovoltaicas de CdTe se necesita de investigación de frontera, especialmente enfocada a escalas atómicas. Sin embargo, considerando la complejidad de los experimentos a escala atómica, solamente los estudios computacionales de primeros principios permiten revelar y llevar a cabo aquel nivel de detalle. Hemos realizado un estudio cuantitativo a través de cálculos de primeros principios para encontrar y establecer la energía de formación de la vacancia de teluro, VTe. El marco de trabajo más común para calcular energías de formación es conocida como la aproximación de frontera periódica (PBC, por sus siglas en ingles), la cual replica periódicamente una celda dada. El problema radica en la selección del tamaño de la supercelda, puesto que en estados cargados habrá una falsa interacción Coulombiana entre un defecto y sus réplicas periódicas que decae al aumentar la distancia entre defectos. Una alternativa para esta aproximación es la aproximación QM/MM. En dicha aproximación utilizamos una fracción del cristal (llamada cluster) la cual se trabaja a nivel cuántico (región QM) y que luego es incrustada en un conjunto de cargas puntuales que se trabajan a nivel clásico (región MM). Estas cargas puntuales son ajustadas de forma de reproducir los mismos efectos que un cristal infinito en el centro del cluster. En este trabajo hemos utilizado ambas aproximaciones y hemos llegado a establecer valores más seguros para la vacancia de teluro. The generation of energy through solar radiation is one the most promising technologies for a sustainable future. In particular, photovoltaic technologies of cadmium telluride (CdTe) are still far from reaching their maximum efficiency, but have also managed to compete in price with respect to traditional crystalline silicon photovoltaic cells. In the photovoltaic cells of CdTe frontier research is needed, especially focused on atomic scales. However, consider- ing the complexity of the atomic-scale experiments, only the computational studies of first principles calculations reveal and carry out this level of detail. We have performed a quantitative study through first principles calculations for finding and establishing the tellurium vacancy formation energy, VTe. The most common framework for calculating formation energies is known as the periodic boundary conditions approxima- tion (PBC), which periodically replicates a given cell. The problem lies in the selection of the super-cell size, since in charged states there will be a spurious Coulomb interaction between one defect and its periodic replicas which decays as the distance between defects increases. An alternative to this approach is the QM/MM approach. In this approximation we use a fraction of the crystal (called cluster) which is treated at the quantum level (QM region) and then is embedded in a set of point charges that are treated at the classical level (MM region). These point charges are adjusted to reproduce the same effects as an infinite crystal at the center of the cluster. In this work we have used both approaches and we have come to establish more secure values for the tellurium vacancy.
Este trabajo ha sido financiado a través del proyecto FONDECYT 1130347

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Blaudeau, Jean-Philippe. "Ab initio calculations of metal-metal complexes using relativistic effective core potentials /." The Ohio State University, 1993. http://rave.ohiolink.edu/etdc/view?acc_num=osu1487847309052921.

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Markevich, Alexander. "Ab-initio calculations of diffusion barriers of small vacancy clusters in silicon." Master's thesis, Universidade de Aveiro, 2009. http://hdl.handle.net/10773/2288.

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Mestrado em Ciência e Engenharia de Materiais
Esta tese apresenta os resultados de um programa de investigação sobre a difusão da lacuna, bi-lacuna e tri-lacuna em silício utilizando simulações numéricas pelo método da teoria do funcional da densidade. Este método está implementado na forma de um programa informático referido como AIMPRO (Ab Initio Modelling PROgram). Para o cálculo dos pontos cela dos mecanismos de difusão foi usado o método “Nudged Elastic Band”. As condições fronteira dos problemas foram impostas recorrendo à utilização de agregados esféricos de silício com 275 atomos, cuja superfície foi saturada por ligações Si-H. As lacunas foram então introduzidas no centro destes agregados. Os valores calculados das barreiras de difusão para a lacuna simples e para a bi-lacuna são respectivamente 0.68 e 1.75 eV. Estes valores apresentam um acordo razoável com os obtidos experimentalmente e obtidos em outros cálculos anteriores. A barreira de difusão da tri-lacuna foi, de acordo com a literatura disponível, calculada pela primeira vêz. O mecanismo de difusão mais favorável apresenta uma barreira de 2.2 eV. No seguimento dos resultados para a lacuna e bi-lacuna, pensamos que este resultado sobrestima a barreira em cerca de 0.25 eV, colocando a nossa melhor estimativa em 1.9- 2.0 eV. Varias fontes de erro nos resultados são comentadas, assim como são sugeridas várias formas de as evitar. ABSTRACT: This work presents the results of a computational investigation into the diffusion of the single vacancy (V) and small vacancy clusters, divacancy (V2) and trivacancy (V3), in silicon. The calculations were performed principally using local density functional theory as implemented by the AIMPRO (Ab Initio Modelling PROgram) code. The Nudged Elastic Band Method was used for elucidating diffusion paths and obtaining the energy barriers for diffusion of the defects considered. Based on ab-initio calculations with H-terminated Si clusters with 275 host atoms, diffusion paths for neutral Vn (n = 1 to 3) defects were found. Calculated values of the activation energy for the diffusion of the Si vacancy and divacancy are 0.68 and 1.75 eV, respectively. These values are in a reasonable agreement with those derived from experimental and previous ab-initio modelling studies. The diffusion of trivacancy in Si has been modelled for the first time. The diffusion barrier of V3 along the proposed diffusion path was found to be about 2.2 eV. This result comes overestimated as the experimental data indicates that the values of diffusion barriers for divacancy and trivacancy in Si should be similar. Probable sources of the calculation errors have been considered and possible ways to surmount these difficulties are proposed.

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Deflorian, Sergio. "Ab initio calculations of hadronic and electromagnetic reactions for few-body systems." Doctoral thesis, Università degli studi di Trento, 2016. https://hdl.handle.net/11572/369266.

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A study of methods in few-body nuclear physics is presented, in particular for the study of the photodisintegration cross section of 3He at low energies, and for the determination of phase shifts in low-energy three-body scattering. A possible extension of the methods considered to the study of a five-body problem is investigated.

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Deflorian, Sergio. "Ab initio calculations of hadronic and electromagnetic reactions for few-body systems." Doctoral thesis, University of Trento, 2016. http://eprints-phd.biblio.unitn.it/1750/1/tesi.pdf.

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A study of methods in few-body nuclear physics is presented, in particular for the study of the photodisintegration cross section of 3He at low energies, and for the determination of phase shifts in low-energy three-body scattering. A possible extension of the methods considered to the study of a five-body problem is investigated.

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Machado, Charry Fabio Eduardo. "First principles calculations of surfaces and layered materials." Doctoral thesis, Universitat Autònoma de Barcelona, 2007. http://hdl.handle.net/10803/3273.

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En este trabajo se han realizado cálculos de primeros principios para estudiar las propiedades físicas de superficies y materiales laminares. Los cálculos se basan en la obtención de las propiedades electrónicas por medio de la Teoría del Funcional de la Densidad, con la que se obtienen la energía y fuerzas atómicas para cada sistema estudiado. De esta forma, se realizaron cálculos de optimización estructural y de dinámica molecular, que proporcionan información sobre las estructuras de equilibrio y la dinámica atómica en función de las condiciones externas (tales como presión y temperatura). Los cálculos realizados se han centrado en diferentes sistemas con interés experimental, siempre en estrecha colaboración con distintos grupos experimentales. En el campo de superficies, se han estudiado problemas relacionados con el crecimiento de láminas delgadas de Cobre para metalización de circuitos microelectrónicos, la adsorción de fullerenos sobre superficies de Germanio, y la medición de ondas de densidad de carga mediante microscopía de efecto túnel en bronces azules. En materiales laminares, el trabajo se ha centrado en comprender el efecto de la presión sobre las propiedades estructurales y electrónicas de semiconductores laminares III-VI, así como en explicar la aparición de nuevas fases no-laminares para varios de estos sistemas a altas presiones.
In this work we have made first-principles calculations to study the physical properties of surfaces and layered materials. The calculations are based on obtaining the electronic properties through the Density Functional Theory, with which the energy and atomic forces for each system studied are derived. Thus, structural optimization calculations and molecular dynamics were carried out. They provide information about the equilibrium structure and the atomic dynamic as a function of external conditions (such as temperature and pressure). Calculations have focused on different systems with experimental interest, always in strong collaboration with different experimental groups. In the field of surfaces we have been studied problems associated with the growth of thin films of copper for metallization of microelectronic circuits, the adsorption of fullerenes on Germanium surfaces, and the measurement of charge density waves by scanning tunneling microscopy in bronze blue. In layered materials, the work has focused on understanding the effect of pressure on the structural and electronic properties of layered semiconductor III-VI, as well as explaining the emergence of new no-layered phases for several of these systems at high pressures.

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Wann, Derek A. "Gas-phase structures of molecules containing heavy p-block elements." Thesis, University of Edinburgh, 2005. http://hdl.handle.net/1842/1209.

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Gas-phase electron diffraction (GED) is the method of choice for determining the structures of molecules containing between two and 100 atoms, free from intermolecular interaction. However, for many molecules it becomes necessary to augment the experimental GED data with information from other sources. The SARACEN method, used routinely at Edinburgh when determining structures, allows computed parameters from ab initio and density functional theory (DFT) calculations to be used as extra data in the GED refinement process. This thesis describes the determinations of the gas-phase structures of molecules that contain heavy p-block elements, including examples from Groups 13, 14, 15 and 16. Each of the compounds studied was solid at room temperature, requiring heating to produce a suitable vapour pressure and vaporisation rate and testing the existing electron diffraction apparatus to its limits. Use was made of a new heated reservoir, recently developed in Edinburgh by a previous PhD student, which has allowed compounds to be studied that were previously inaccessible. The molecules that were studied during the course of this degree are: In(P3C2But2), In(P2C3But3), Sn(P2C2But2), Sb2(C6F6)3, Bi2(C6F6)3, Se(SCH3)2 and Te(SCH3)2. While determining the structures of these molecules, accurate theoretical geometries have been obtained using both ab initio and DFT methods. As a result a better understanding has been achieved of which methods are suitable for use in calculating the structures of molecules with heavy p-block elements. The use of pseudopotentials as opposed to all-electron basis sets proved necessary when performing calculations on such large molecules with heavy atoms. The extent to which these pseudopotentials, especially ones that consider very few electrons to be in the valence shell of an atom, can affect the calculated geometries has been shown to be considerable. In addition, methods being developed to compute vibrational corrections for gas-phase structure determination have been extended to the crystalline phase. Molecular dynamics simulations have been used to derive the effects of vibrations on average nuclear positions, relative to equilibrium positions. The differences, when applied to coordinates obtained experimentally by neutron diffraction yield experimental equilibrium structures.

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Day, Stephen Paul. "Approaches to ab-initio GIPAW-DFT calculations of NMR parameters in disordered materials." Thesis, University of Warwick, 2015. http://wrap.warwick.ac.uk/78781/.

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The use of ab initio Density Functional Theory (DFT) to calculate key Nuclear Magnetic Resonance (NMR) parameters has been shown to be very successful in a variety of cases. These calculations allow one to extract meaningful data from NMR measurements by providing a foundation for spectral peak assignment. However, first principle calculations for disordered systems, typically based on a single realisation of the disorder, are inadequate if the NMR parameters depend sensitively on the location of the disordered species. In this thesis, a number of different approaches for characterising disorder in solids are presented. The aim of which is to overcome current challenges regarding the computational cost of conventional supercell approaches that make it difficult to perform a direct study of the complete configurational ensemble for any supercell with a sufficient simulation cell. A case study is presented for the Ge-based apatite La7.5Ca2.5Ge6O25.75 that shows that the number of configurations one needs to consider can be vastly reduced by exploiting the symmetry of the system over a wholly enumerative approach, although exhaustive statistical averaging of the atomic positions required to reproduce the atomic resolution afforded by the solid-state NMR (ssNMR) measurement makes this problem intractable via this methodology. The sodium potassium niobate system (NaxK1-xNbO3) is studied across a series of compositions between the ordered KNbO3 and NaNbO3 end-members. This novel material exhibits purely atomic position / permutation disorder that is reflected in initial 23Na and 93Nb MAS NMR studies, but the true explanation of the disorder described by this data is not well understood. The Special Quasi-random Structure (SQS) approach to studying this disorder is presented as a computationally cheaper alternative to the supercell approach. It is noted that further studies are required to assess whether this is an adequate description of the NaxK1-xNbO3 system due the complications of modelling the complex tilting patterns exhibited by these structures. A combined ssNMR and GIPAW-DFT approach is reported to resolve the complex disorder within the vaterite polymorph of calcium carbonate. The computational data for the various structural candidates in the literature is utilised to simulate the highly sensitive DOR data, thereby elevating the predictive capability of this complementary approach to substantiate the stacking model of vaterite that views the material as a dynamic system under ambient conditions.

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Corsetti, Fabiano. "On the properties of point defects in silicon nanostructures from ab initio calculations." Thesis, Imperial College London, 2012. http://hdl.handle.net/10044/1/9754.

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In this thesis we apply a variety of computational methods based on density-functional theory (DFT) to the study of defect centres in bulk silicon and silicon nanostructures. Firstly, we discuss the system-size convergence of point defect properties in the supercell method for deep-level defects in bulk silicon; we consider both the vacancy and gold impurity. For the vacancy, we investigate systematically the main contributions to the finite size error that lead to the well-known slow convergence with respect to system size of defect properties, and demonstrate that different properties of interest can benefit from the use of different k-point sampling schemes. We also present a simple and accurate method for calculating the potential alignment correction to the valence band maximum of charged defect supercells by using maximally-localised Wannier functions, and show that the localised view of the electronic structure provided by them gives a clear description of the nature of the electronic bonding at the defect centre. For the gold impurity, we show that the system becomes a non-spin-polarised negative-U centre due to the effect of Jahn-Teller distortion, thus providing a simple explanation for the absent electron paramagnetic resonance signal for gold in silicon. The calculated transition levels are found to be in excellent agreement with experimental measurements. We then investigate the segregation of arsenic impurities in silicon close to an interface with amorphous silica. We employ a multiscale approach, generating a realistic disordered interface structure from Monte Carlo simulation, with a continuous random network model of the system parametrised from DFT. We calculate the segregation energy using DFT for a large number of substitutional sites encompassing all the oxidation states of silicon, and show that the results can be understood with a minimal model based only on the local strain and volume of the defect site.

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Rayson, Mark James. "On advances in the kernel and functionality of ab initio electronic-structure calculations." Thesis, University of Newcastle Upon Tyne, 2005. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.413143.

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Ullrich, Susanne. "Conformers and non-covalent interactions studied by laser spectroscopies and Ab initio calculations." Thesis, University of York, 2001. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.247030.

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Hyams, Peter Alan. "Ab initio calculations of molecular structure and properties using the spin-coupled wavefunction." Thesis, University of Bristol, 1989. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.279733.

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Cole, John Philip. "Ab initio calculations of rates and product state distributions of gas phase reactions." Thesis, University of Bristol, 2003. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.289619.

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Langlois, Jean-Marc Goddard William A. "New methods for ab initio quantum mechanical calculations in molecular and crystalline systems /." Diss., Pasadena, Calif. : California Institute of Technology, 1994. http://resolver.caltech.edu/CaltechETD:etd-12042007-081615.

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Munzarová, Markéta. "Quantum chemical calculations of EPR parameters for transition metal complexes." [S.l. : s.n.], 2001. http://www.bsz-bw.de/cgi-bin/xvms.cgi?SWB9587938.

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Dissertations / Theses on the topic 'Ab initio calculations'

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