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1	Applications of density functional theory for modeling metal-semiconductor contacts, reaction pathways, and calculating oxidation states Posysaev, S. (Sergei) 30 November 2018 (has links) Abstract Density functional theory (DFT) is a well-established tool for calculating the properties of materials. The volume of DFT-related publications doubles every 5–6 years, which has resulted in the appearance of continuously growing open material databases, containing information on millions of compounds. Furthermore, the results of DFT computations are frequently coupled with experimental ones to strengthen the computational findings. In this thesis, several applications of DFT related to physics and chemistry are discussed. The conductivity between MoS₂ and transition metal nanoparticles is evaluated by calculating the electronic structure of two different models for the nanoparticles. Chemical bonding of Ni to the MoS₂ host is proven by the system’s band alignment. To meet the demand for cleaner fuel, the applicability of the (103) edge surface of molybdenum disulfide in relation to the early stages of the hydrodesulfurization (HDS) reaction is considered. The occurrence of the (103) edge surface of molybdenum disulfide in the XRD patterns is explained. A method for calculating oxidation states based on partial charges using open materials databases is suggested. We estimate the applicability of the method in the case of mixed valence compounds and surfaces, showing that DFT calculations can be used for the estimation of oxidation states. / Tiivistelmä Tiheysfunktionaaliteoria (density functional theory, DFT) on yleisesti käytetty työkalu laskennallisessa materiaalitutkimuksessa. DFT:llä tuotettujen julkaisujen määrä kaksinkertaistuu 5–6 vuoden välein, minkä johdosta käytettävissä on jatkuvasti kasvava määrä avoimia materiaalitietokantoja, joihin on talletettu miljoonien yhdisteiden ominaisuuksia. DFT-laskujen tuloksia täydennetään myös usein kokeellisilla tuloksilla. Tässä työssä tarkastellaan tiheysfunktionaaliteorian sovelluksia fysiikassa ja kemiassa. MoS₂:n ja metallisten nanopartikkelien välistä johtavuutta on tutkittu mallintamalla erilaisia nanopartikkeleita. Nikkelin ja MoS₂:n välinen kemiallinen sidos selittyy systeemin energiavöiden kohdistumisella. MoS₂:n (103)-pinnan soveltuvuutta rikinpoistoreaktion varhaisissa vaiheissa on tutkittu tarkoituksena löytää uusia menetelmiä puhtaan polttoaineen tuottamiseksi. Myös (103)-pinnan esiintyminen röntgendiffraktiokuvissa selitetään. Työssä on myös esitetty menetelmä hapetustilojen laskemiseksi tietokannoista löytyvien laskettujen varausjakaumien avulla. Menetelmän soveltuvuutta on tarkasteltu erilaisille yhdisteille ja pinnoille. Tämä tarkastelu osoittaa, että DFT-tuloksia voidaan käyttää hapetustilojen laskemiseen. Bader charge density functional theory molybdenum disulfide oxidation state reaction pathway Bader-varaus hapetustila molybdeenidisulfidi reaktiopolku tiheysfunktionaaliteoria
2	Properties of binary oxides:a DFT study Miroshnichenko, O. (Olga) 14 June 2019 (has links) Abstract Titanium dioxide nanoparticles are used in an enormous amount of applications. Their properties are different from bulk TiO₂ and are affected by adsorbates that are unavoidably present on the surface. In this thesis, the effect of OH and SO₄ groups (the adsorbants present on the surface during manufacturing) on the properties of anatase-structured TiO₂ nanoparticles is studied. It was found that the above mentioned groups change both the geometric and electronic structure of nanoparticles, resulting in changes in the photoabsorption spectrum. Bader charges are calculated using electron density from Density Functional Theory calculations. They can be used for determination of the oxidation state of the atom. The relation between computed partial charges and oxidation states for binary oxides using data from open materials database has been demonstrated in this work using a linear regression. The applicability of the oxidation state determination by Bader charges for mixed valence compounds and surfaces is considered. / Tiivistelmä Titaanidioksidinanopartikkeleita käytetään lukuisissa sovelluksissa. Niiden ominaisuudet poikkeavat kiinteän TiO₂:n ominaisuuksista, ja niihin vaikuttavat pinnalle väistämättä absorboituvat aineet. Tässä työssä on tutkittu OH- ja SO₄-ryhmien vaikutusta anataasirakenteisten TiO₂-nanopartikkelien ominaisuuksiin. Tällaisia ryhmiä esiintyy yleisesti nanopartikkelien pinnalla valmistusprosessien aikana. Työssä havaittiin, että nämä ryhmät muuttavat nanopartikkelien rakenteellisia ja sähköisiä ominaisuuksia, ja siten vaikuttavat myös fotoabsorptiospektriin. Baderin varaukset voidaan laskea käyttäen tiheysfunktionaaliteoriaan perustuvista laskuista saatavaa elektronitiheyttä. Niitä voidaan käyttää atomin hapetustilan laskemiseen. Tässä työssä on osoitettu, että binääristen oksidien tapauksessa laskettujen osittaisvarauksien ja hapetustilan välillä on yhteys. Tämä yhteys voitiin osoittaa käyttämällä lineaarista regressiota. Työssä tarkastellaan myös menetelmän soveltuvuutta hapetustilojen määrittämiseen sekavalenssiyhdisteille ja pinnoille. / Original papers Original publications are not included in the electronic version of the dissertation. Miroshnichenko O., Auvinen S., & Alatalo M. (2015). A DFT study of the effect of OH groups on the optical, electronic, and structural properties of TiO₂ nanoparticles. Phys. Chem. Chem. Phys., 17, 5321–5327. https://doi.org/10.1039/c4cp02789b Miroshnichenko O., Posysaev S., & Alatalo M. (2016). A DFT study of the effect of SO4 groups on the properties of TiO₂ nanoparticles. Phys. Chem. Chem. Phys., 18, 33068–33076. https://doi.org/10.1039/c6cp05681d http://jultika.oulu.fi/Record/nbnfi-fe201707037608 Posysaev S., Miroshnichenko O., Alatalo M., Le D., & Rahman T.S. (2019). Oxidation states of binary oxides from data analytics of the electronic structure. Comput. Mater. Sci., 161, 403–414. https://doi.org/10.1016/j.commatsci.2019.01.046 Bader charge data analytics density functional theory electronic structure nanoparticles open materials databases oxidation state photoabsorption titanium dioxide Baderin varaus avoimet materiaalitietokannat data-analytiikka elektronirakenne fotoabsorptio hapetustila nanopartikkelit tiheysfunktionaaliteoria titaanidioksidi
3	Efeitos da inserção de íons de Cr4+/2+ na matriz cristalina do Bi12GeO20 : estudo de primeiros princípios / Effects of the insertion of Cr ions on the crystalline matrix of Bi12GeO20: a first principles study Santana, Lucas Barreto 26 February 2018 (has links) Conselho Nacional de Pesquisa e Desenvolvimento Científico e Tecnológico - CNPq / Bi12GeO20 (BGO) belongs to the family of sillenite crystals BMO, where M = Ge, Si, Ti. These compounds exhibit remarkable photorefractive e ect and therefore are used in the development of information and image storage technologies, holography, ampli cation of luminous signals and dynamic interferometry. One of the strategies used to enhance the properties of interest of these sillenites is doping. The defects can create photorefractive centers in the matrix, introducing energy levels within the gap, in uencing the electronic and optical properties of the selenites. Experimental work reported a curious behavior when using transition metal ions (TMI) as dopants. Most of the TMIs, including Cr ions, are allocated at the high symmetry site Ge4+, with the exception of Cu2+ which enters into the matrix at the low symmetry site of Bi3+. This is a surprising fact due to the di erence between ionic radii and charge states of the dopants and the substitution ion Ge4+. In this work the LAPW method, based on the DFT theory and implemented in the WIEN2k program, was used to study the electronic, structural and energetic properties of pure BGO and doped BGO with chromium ions. In the study of doped cases, Cr ions were inserted at the substitutional sites of Ge4+ and Bi3+ The calculations were performed for neutral and charged systems. The approximations for correlation and exchange e ects were made through GGA-PBE and mBJ potentials. Were performed calculations of lattice parameter optimization, relaxation of atomic positions, state density, Bader charge and formation energies of defects. It was possible to nd the lattice parameter, and the band gap energy os the BGO pure, to analyse the way how the neighbourhood of the substitutional site behaves with the presence of the defect and nd the states that populate the valence and conduction bands of the studies cases. These data were taking into account to measure the ions valence. The results of the modeling showed that Cr prefers to accommodate in the BGO matrix with Cr3+/4+ valences. The preferential accommodation site of Cr3+ is Bi3+, which didn't meet with what has been reported experimentally in the literature. / O Bi12GeO20 (BGO) pertence a fam lia de cristais silenitas do tipo BMO, onde M = Ge, Si, Ti. Tais compostos apresentam um not avel efeito fotorrefrativo e por isso s~ao utilizados no desenvolvimento de tecnologias de armazenamento de informa c~oes e imagens, hologra a, amplia c~ao de sinais luminosos e interferometria din^amica. Uma das estrat egias utilizadas para potencializar as propriedades de interesse dessas silenitas e a dopagem. Os defeitos podem criar centros fotorrefrativos na matriz, introduzindo n veis de energias dentro do gap e in uenciar nas propriedades eletr^onicas e opticas das silenitas. Trabalhos experimentais relataram um comportamento curioso ao se utilizar ons de metais de transi c~ao (TMI) como dopantes. A maior parte dos TMIs, incluindo os ons de Cr, s~ao alocados no s tio de alta simetria Ge4+, com exce c~ao do Cu2+ que se insere na matriz no s tio de baixa simetria do Bi3+. Esse e um fato surpreendente devido a diferen ca entre raios i^onicos e estados de carga dos dopantes e do on substitucional Ge4+. Neste trabalho foi utilizado o m etodo LAPW, baseado na teoria DFT e implementado no programa WIEN2k, para estudar as propriedades eletr^onicas, estruturais e energ eticas do BGO puro e dopado com ons de cromo. No estudo de casos dopados, os ons de Cr foram inseridos nos s tios substitucionais Ge4+ e Bi3+. Os c alculos foram executados para sistemas neutros e carregados. As aproxima c~oes para os efeitos de correla c~ao e troca foram feitas atrav es do funcional GGA-PBE e do potencial mBJ. Foram realizados c alculos de otimiza c~ao de par^ametro de rede, relaxa c~ao de posi c~oes at^omicas, densidade de estados, carga de Bader e energias de forma c~ao de defeito. Foi poss vel encontrar o par^ametro de rede, a energia de gap do BGO puro, analisar a forma como a vizinhan ca do s tio substitucional se comporta com a presen ca do defeito e encontrar os estados que populam as bandas de val^encia e condu c~ao dos casos estudados. Esses dados foram levados em conta para aferir a val^encia dos ons. Os resultados das modelagens mostraram que o Cr prefere se acomodar na matriz do BGO com val^encias Cr3+/4+. O s tio de acomoda c~ao preferencial do Cr3+ e o Bi3+, o que vai de encontro ao que foi relatado experimentalmente na literatura. / São Cristóvão, SE Bi12GeO20 BGO Silenitas Dopagem Cromo (Cr) Propriedades eletrônicas Densidades de estado Carga de Bader Energia de formação Sítio de acomodação Sillenite Doping Chrome (Cr) Electronic properties Densities of stae Bader charge Formation energy Accomodation sites CIENCIAS EXATAS E DA TERRA::FISICA
4	Cobalt porphyrins on coinage metal surfaces - adsorption and template properties / Porphyrine de cobalt dans surfaces métalliques - propriété d’adsorption et de template Houwaart, Torsten 08 July 2014 (has links) Cette thèse est une étude théorique sur la interface de porphyrine de cobalt avec des surfaces métalliques avec le code VASP DFT. Le cadre DFT nécessaire a été introduit dans le chapitre 1. La structure de la jBardeen, une programme ecrit en Java, pour la simulation de la STM est expliqué dans le chapitre 2 et le code source est jointe en annexe. Une étude de l'adsorption de CoTPP sur les surfaces métalliques a été entrepris dans le chapitre 3. Différents paramètres de calcul ont été évalués: Le site d'adsorption et de la géométrie à la fois la molécule et la surface ont été étudiés par rapport à la xc-fonctionnel et correction de la dispersion utilisée. Une adsorption site le plus stable est identifié. Par conséquent, ce site plus stable a été étudiée pour sa structure électronique. Calculés images STM avec le code jBardeen ont été comparés avec une experimentation de CoTPP Cu sur une surface (111) avec une couverture sous monocouche. Dans le chapitre 4, un adatome Fe a été présenté à la CoTPP sur Ag système (111). Trois sites de liaison symétrique différentes pour l'atome Fe ont été identifiés sur le macrocycle, marqué les , bi-, brd- et bru-positions. Un moment magnétique pouvait être attestée qui a été principalement situé sur l'atome Fe. Voies possibles entre les quatre, symétriquement équivalentes, sites bi- ont été étudiées avec des méthodes différentes. Simples calculs dans le vacuum et calculs de la “Nudged Elastic Band” (NEB) de l'ensemble du système a révélé une hauteur de barrière légèrement au-dessus de 0,2 eV allant de position bi à la posititon brd. Une analyse de vibration a montré que la commutation de l'atome Fe est susceptible, lorsqu'il est perturbé hors d'équilibre dans les positions brd et bru. / This thesis is a theoretical study on the cobalt porphyrin - coinage metal surface interface with the DFT code VASP. The necessary DFT framework has been introduced in chapter 1. The structure of the Java program jBardeen for STM simulation is explained in chapter 2 and the source code is attached as Appendix. A study of the adsorption of CoTPP on coinage metal surfaces has been undertaken in chapter 3. Different parameters of the calculation have been evaluated: the adsorption site and the geometry of both the molecule and surface have been investigated with respect to the xc-functional and dispersion correction used. A most stable adsorption site -bridge down- is identified. Consequently, this most stable site was investigated for its electronic structure. Calculated STM images with the jBardeen code were compared with an experiment of CoTPP on a Cu(111) surface with sub monolayer coverage. In chapter 4 an Fe adatom was introduced to the CoTPP on Ag(111) system. Three symmetrically different binding sites for the Fe atom were identified on the macrocycle, labelled the bi-, brd- and bru-positions for bisector, bridge down and bridge up respectively. A magnetic moment could be evidenced which was mainly located on the Fe atom. Possible pathways between the four symmetrically equivalent bisector sites were investigated with different methods. Single point calculations in vacuum and Nudged Elastic Band (NEB) of the whole system revealed a barrier height of slightly above 0.2 eV going from bi- to the brd-position. A vibrational analysis showed that switching of the Fe atom is likely, when perturbed out of equilibrium in the brd- and bru- positions. Porphyrine de Cobalt CoTPP Pophyrine Microscope à effet tunnel STM DFT Surfaces métalliques Adsorption Templates Étude théorique Interface métal molécule VASP JBardeen Programme Java Site d'adsorption Géométrie d'adsorption Correction de dispersion Xc-fonctionnel D2 Grimmes potentiel Grimmes D2 Structure électronique Cu(111) Ag(111) Fe adatome Site de liaison Moment magnétique Couplage magnétique Dynamique de commutation NEB Analyse de vibration Analyse de charge Bader PDOS Cobalt-Tetra-Phenyl-Porphyrin CoTPP Porphyrins Scanning Tunneling Microscopy STM Density Functional Theory DFT Coinage metal surfaces Adsorption Templating Theoretical study Molecule metal interface VASP JBardeen Java program Adsorption site Adsorption geometry Xc-functional Dispersion correction D2 Grimmes potential Grimmes D2 Electronic structure Cu(111) Ag(111) Fe adatom Binding site Magnetic moment Magnetic coupling Switching dynamics NEB Nudged Elastic Band Vibrational analysis Bader charge analysis PDOS Projected Density of States

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