|
|
Structure and dynamics of electronic defects in liquid water
Maršálek, Ondřej
Title: Structure and dynamics of electronic defects in liquid water Author: Ondřej Maršálek Institute: Institute of Organic Chemistry and Biochemistry, Academy of Sciences of the Czech Republic Supervisor: prof. Mgr. Pavel Jungwirth, DSc. Supervisor's e-mail address: pavel.jungwirth@uochb.cas.cz Abstract: In this thesis we present ab inito molecular dynamics simulations of two different electronic defects in water. Photoionization of liquid water produces a cationic hole, which undergoes ultrafast dynamics and forms the hydrated proton and the hydroxyl radical as its products. We study both the dynamics and spectroscopy of this process. The hydrated electron is a key intermediate in radiation chemistry of aqueous systems. We simulate its equilibrium properties in anionic water clusters as well as the dynamics of vertical electron attachment to cold and warm clusters. The hydrated electron reacts with a hydrated proton to form a hydrogen atom. We examine this reaction at a finite temperature in a larger cluster as well as in more detail in a smaller cluster. Because both of the electronic defects studied here are challenging open-shell species, we put emphasis on benchmarking and testing our computational setup. Six published articles are attached to the thesis. Keywords: density functional theory,...
|
|
|
Theoretical Study of Influence of Silanol Nest Defects on Hydrolysis of Zeolite Chabazite
Vacek, Jaroslav ; Grajciar, Lukáš (advisor) ; Fišer, Jiří (referee)
This thesis is focused on theoretical study of influence of the silanol nest defects on the hydrolysis of zeolite Chabazite under harsh steaming conditions. The motivation of the thesis was a recent experiment proving that the silanol nest defect enhances the hydrolysis of a zeolite. The harsh steaming conditions have been chosen as some important technological processes involving zeolites require high temperatures and have water vapour present. The study was performed by using density functional theory calculations. To investigate the influence of the defect two models were used a reference pristine model and a defected model containing the silanol nest defect. The two models were pure siliceous Chabazite periodical models with supercell containing 36 and 35 Si tetrahedra respectively. A multi-step hydrolysis leading to detachment of a Si(OH)4 cluster from the zeolite, known as total desilication, was calculated for the two models. Multiple possible paths of the hydrolysis were discovered, compared and discussed on both models. Both the most favourable hydrolysis paths of the two model as well as their arithmetic means were compared. The experimentally set expectations that a silanol nest defect enhances the hydrolysis of the zeolite have been met.
|
|
|
Theoretical investigation of water-zeolite interactions under steaming conditions
Benešová, Tereza ; Heard, Christopher James (advisor) ; Fišer, Jiří (referee)
The thesis is focused on theoretical study of hydrolysis and isotopic oxygen exchange in zeolite chabazite under steaming conditions. The theoretical study was performed by the methods of computational chemistry, namely density functional theory. Reactions of water with zeolites were investigated within the periodic model with chabazite supercell consisting of 36 Si/Al tetrahedra. Reactivity was investigated for one or two water molecules corresponding to the conditions relevant to high-temperature steaming. Relevant mechanisms of isotopic oxygen exchange were found and their competitiveness with hydrolysis was discussed.
|
|
|
Theoretical Investigation of Properties of 3D and 2D Zeolites
Ho, Viet Thang ; Nachtigall, Petr (advisor) ; Fišer, Jiří (referee) ; Cwiklik, Lukasz (referee)
Zeolites have been widely used in many different fields including catalysis, adsorption and separation, ion exchange, or gas storage. Conventional zeolites have three- dimensional (3D) structures with microporous channel system; typical pore sizes are well below 1 nanometer, therefore, diffusion limitation plays important role in many process and bulkier reactants (or products) cannot enter (or leave) the zeolite channel system. Two-dimensional (2D) zeolites prepared in last years can lift all diffusion limitation and they thus offer a very attractive alternative to conventional 3D zeolites. 2D zeolites attracted considerable attention on the experimental side; however, understanding of 2D zeolites based on computational investigation or on a combination of experimental and computational investigation is limited. A motivation for the computational work presented here is to improve our understanding of properties of 2D zeolites based on computational investigation. The originality of the research presented herein is in the strategy: we carried out systematic investigation of properties of corresponding 2D and 3D zeolites and we focus on the identification of similarities and differences. The most important zeolite properties, i.e., presence of Brønsted and Lewis acid sites, are investigated. A number of...
|
|
|
Computational investigation of adsorption of saturated and unsaturated hydrocarbons in CPO-27 Metal-Organic Framework
Smetanová, Tereza ; Nachtigall, Petr (advisor) ; Bludský, Ota (referee)
Title: Computational investigation of adsorption of saturated and unsaturated hydrocarbons in CPO-27 Metal-Organic Framework Abstract: The adsorption of hydrocarbons on coordinatively unsaturated sites (cus) in CPO-27 Metal-Organic Framework (MOF) was investigated computationally. Different levels of density functional theory (DFT), including vdW-DF2, PBE, DFT-D2 functionals, were used and their performance was compared to a reference method DFT/CC and available experimental data. The adsorption properties of Cu and Mg containing CPO-27 for ethane, ethylene, propane and propylene separations were investigated and discussed. Keywords: adsorption, metal-organic frameworks, density functional theory, coordinatively unsaturated sites, open metal sites
|
|
|
Structure, dynamics and reactivity of the hydrated electron
Uhlig, Frank ; Jungwirth, Pavel (advisor) ; Pittner, Jiří (referee) ; Sebastiani, Daniel (referee)
Structure, dynamics and reactivity of the hydrated electron Frank Uhlig In this work, one of the products of ionization of water, namely the hydrated electron, has been investigated. The hydrated electron is a key-intermediate in aqueous radiation chemistry. Although known to exist for over 50 years, its structure remained elusive and under discussion up to the present day. We show in this work, that we can obtain a faithful picture of the hydrated electron, its equilibrium structure, dynamics after attachment to water, and its reactivity, using ab initio methods. To this end, small cluster models and extended bulk and slab geometries of water including an excess electron have been investigated.
|
|
|
Structure and dynamics of electronic defects in liquid water
Maršálek, Ondřej
Title: Structure and dynamics of electronic defects in liquid water Author: Ondřej Maršálek Institute: Institute of Organic Chemistry and Biochemistry, Academy of Sciences of the Czech Republic Supervisor: prof. Mgr. Pavel Jungwirth, DSc. Supervisor's e-mail address: pavel.jungwirth@uochb.cas.cz Abstract: In this thesis we present ab inito molecular dynamics simulations of two different electronic defects in water. Photoionization of liquid water produces a cationic hole, which undergoes ultrafast dynamics and forms the hydrated proton and the hydroxyl radical as its products. We study both the dynamics and spectroscopy of this process. The hydrated electron is a key intermediate in radiation chemistry of aqueous systems. We simulate its equilibrium properties in anionic water clusters as well as the dynamics of vertical electron attachment to cold and warm clusters. The hydrated electron reacts with a hydrated proton to form a hydrogen atom. We examine this reaction at a finite temperature in a larger cluster as well as in more detail in a smaller cluster. Because both of the electronic defects studied here are challenging open-shell species, we put emphasis on benchmarking and testing our computational setup. Six published articles are attached to the thesis. Keywords: density functional theory,...
|
|
|
First-principles studies of the electronic and structural properties of Lead Zirconate Titanate (PZT)
Planer, Jakub ; Friák, Martin (referee) ; Bartošík, Miroslav (advisor)
This work is focused on Density Functional Theory (DFT) calculations of oxygen vacancy diffusion barriers in mixed perovskite lead zirconate titanate and its pure counterparts. We found out that barrier heights are different in lead titanate and lead zirconate caused by the different localization of the excess electrons due to the oxygen vacancy formation. Diffusion barriers were also determined for titanium-rich mixed phases and compared to experimental values. This work contributes to clarify unusually low experimentally measured diffusion coefficients in PZT. We found out that the induced vacancy states are forming localized bonds to the lead atoms which causes the oxygen vacancies to become immobile due to the increase of the activation energy of the diffusion process.
|
|
|
Theoretical calculation of stability and electronic structure of Si surfaces
Krejčí, Ondřej ; Kocán, Pavel (advisor) ; Szabová, Lucie (referee)
ÁÒ Ø × ÛÓÖ Á Ö Ý ×ÙÑÑ Ö Þ ¹ Ò Ø Ó Ñ Ø Ó × ÓÖ ÓÑÔÙØ Ø ÓÒ Ò ØÓÑ Ò Ò Ð ØÖÓÒ ×ØÖÙ ØÙÖ Ó ÑÓÐ ÙР׸ ×ÓÐ ×Ø Ø × Ò Ø Ö ×ÙÖ × Ô ÖØ ¹ ÙÐ ÖÐÝ Á ÔÙÖ×Ù Ò× ØÝ ÙÒ Ø ÓÒ Ð Ø ÓÖÝž Ì Ò Á × Ö Ø Ñ Ø Ó Ó Ö ÐÐ × ÑÙÐ Ø ÓÒ Ô Ö ¸ Û × × ÓÒ Ø Ò× ØÝ ÙÒ Ø ÓÒ Ð Ø ÓÖÝž Ï Ø Ö ÐÐ Á Ñ ÓÑÔÙØ Ø ÓÒ× Ó Ø Ð ØÖÓÒ ×ØÖÙ ØÙÖ Ó Ë Ð ÓÒ ÙÐ Ò ÓÑÔÙØ Ø ÓÒ× Ó Ø ØÓÑ Ò Ø Ð ØÖÓÒ ×ØÖÙ ØÙÖ Ó Ö ÓÒ×ØÖÙ Ø ÓÒ× 2×1¸ Ô'2×2µ Ò '4×4µ Ó Ë '½¼¼µ ×ÙÖ ž Á ÓÑÔ Ö ÑÝ Ö ×ÙÐØ× Û Ø ÔÖ ¹ Ú ÓÙ×ÐÝ Ñ Ò ÔÙ Ð × ÓÑÔÙØ Ø ÓÒ× Ò ÜÔ Ö Ñ ÒØ× Ö ž ËÙ × ÕÙ ÒØÐÝ Á Ô Ö ÓÖÑ ËÌÅ × ÑÙÐ Ø ÓÒ× Ó Ø × Ö ÓÒ×ØÖÙ Ø ÓÒ׸ Û Á Ð×Ó ÓÑÔ Ö Û Ø Ø ÜÔ Ö Ñ ÒØ Ð Ø ž ½
|
|
|
Relativistic Theory of Electron Transport in Magnetic Layers
Sýkora, Rudolf ; Turek, Ilja (advisor) ; Šob, Mojmír (referee) ; Drchal, Václav (referee)
Title: Relativistic Theory of Electron Transport in Magnetic Layers Author: Rudolf Sýkora Department / Institute: Institude of Theoretical Physics Supervisor of the doctoral thesis: doc. RNDr. Ilja Turek, DrSc., Department of Condensed Matter Physics Abstract: We review the density-functional theory (DFT) in detail using the Levy Lieb ap- proach. The Kohn Sham scheme is discussed, starting from the simplest spinless non- relativistic case, then including spin and considering potential spin magnetism, and finally deriv- ing the full Kohn Sham Dirac relativistic scheme. The Linear Muffin-Tin Orbital (LMTO) method for electronic-structure calculation is presented, together with mentioning the necessary changes to include the spin-orbit (SO) interaction effects to an otherwise scalar-relativistic (SR) theory. Derivation of an electronic-conductance formula for a layered system is given, based on the Landauer scattering picture and using simple non-equilibrium Green functions. The formal- ism is applied to layered metallic systems of light elements Co, Ni, Cu elements, and to layered systems with a tunnelling barrier, Fe/MgO/Ag and Fe/GaAs/Ag. The effects of the SO interac- tion on the Giant Magnetoresistance (GMR) ratio and/or the Tunnelling Anisotropy Magnetore- sistance (TAMR) for these systems are discussed....
|
guest ::
