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Theoretical Investigation of the Zeolite Hydrolysis under Realistic Conditions
Jin, Mengting ; Grajciar, Lukáš (advisor) ; Chizallet, Céline (referee) ; Piskorz, Witold (referee)
Zeolites are one of the most widely used and one of the most industrially important materials. They are utilized in a variety of commercial applications, particularly in heterogeneous catalysis, adsorption/separations applications and as ion exchangers. Zeolites are stable when exposed to water or water vapor at ambient conditions and exhibit high thermal stability. However, zeolites can be partially or even fully hydrolyzed under certain conditions. This hydrolytic instability of zeolites can be considered both a major problem in some applications and a useful means to tune catalyst properties in the others. However, the thorough studies of the hydrolytic mechanisms under realistic conditions (high water loading, alkaline conditions, high heteroatom concentrations, etc.) and employing realistic models (dynamical simulation of ab initio accuracy) is mostly lacking. This dissertation uses the ab initio calculations to systematically study the hydrolysis mechanism of zeolites under realistic conditions, including: (1) hydrolysis mechanism of germanosilicate zeolite UTL, (2) hydrolysis of siliceous zeolite CHA under alkaline conditions, and (3) identification of the nature of framework-associated Al(Oh) species in aluminosilicate zeolite CHA under wet conditions. The main results obtained are as...
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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.
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Optimizing quantum simulations and the DMRG method
Brandejs, Jan ; Pittner, Jiří (advisor)
Title: Optimizing quantum simulations and the DMRG method Author: Jan Brandejs Department: Department of Chemical Physics and Optics Supervisor: doc. Dr. rer. nat. Jiří Pittner, DSc., J. Heyrovský Institute of Physical Chemistry of the Czech Academy of Sciences Abstract: In this work, we explore the quantum information theoretical aspects of simulation of quantum systems on classical computers, in particular the many- electron strongly correlated wave functions. We describe a way how to reduce the amount of data required for storing the wavefunction by a lossy compression of quantum information. For this purpose, we describe the measures of quantum entanglement for the density matrix renormalization group method. We imple- ment the computation of multi-site generalization of mutual information within the DMRG method and investigate entanglement patterns of strongly correlated chemical systems. We present several ways how to optimize the ground state calculation in the DMRG method. The theoretical conclusions are supported by numerical simulations of the diborane molecule, exhibiting chemically interest- ing electronic structure, like the 3-centered 2-electron bonds. In the theoretical part, we give a brief introduction to the principles of the DMRG method. Then we explain the quantum informational...
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Theoretical Investigation of Low-dimensional Magnetic Materials
Li, Shuo ; Grajciar, Lukáš (advisor) ; Frauenheim, Thomas (referee) ; Jelínek, Pavel (referee)
Low-dimensional (D) materials, such as graphene, transition metal dichalcogenides and chalcogenide nanowires, are attractive for spintronics and valleytronics due to their unique physical and chemical properties resulting from low dimensionality. Emerging concepts of spintronics devices will greatly benefit from using 1D and 2D materials, which opens up new ways to manipulate spin. A majority of 1D and 2D materials is non-magnetic, thus their applications in spintronics are limited. The exploration, design and synthesis of new 1D and 2D materials with intrinsic magnetism and high spin-polarization remains a challenge. In addition, the valley polarization and spin-valley coupling properties of 2D materials have attracted great attention for valleytronics, which not only manipulates the extra degree of freedom of electrons in the momentum space of crystals but also proposes a new way to store the information. The computational investigation of magnetic and electronic properties of low-dimensional materials is the subject of this thesis. We have systematically investigated geometric, electronic, magnetic and valleytronic properties of several 2D and 1D materials by using the density functional theory. These investigations not only theoretically show rich and adjustable magnetic properties of...
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Development and applications of molecular dynamics for molecular spectroscopy
Kessler, Jiří
This Thesis deals with simulations of chiroptical spectra using a combination of molecular dynamics and quantum chemistry. Molecular dynamics was used to explore conformational behaviour of studied systems (proteins), quantum chemistry for calculation of spectral prop- erties. The Quantum chemical methods are limited to relatively small systems. We overcome this problem mostly by a fragmentation of studied systems, when smaller, computationally feasible, fragments are created and used for the quantum chemical calculations. Calculated properties were then transferred to the big molecule. Vibrational Optical Activity (VOA) spectra of poly-L-glutamic acid fibrils (PLGA), insulin prefibrillar form and native globular proteins were studied. The simulated spectra provided satisfactory agreement with the experiment and were used for its interpretation. Experimental Vibrational Circular Dichroism (VCD) spectra of poly-L-glutamic acid fibrils were only qualitatively reproduced by the simulation. We could reproduce the major amide I band and a smaller negative band associated with the side chain carboxyl group. Our simulation procedure was then extended to a set of globular proteins and their Raman Optical Activity (ROA) spectra. Here we achieved an exceptional precision. For example, we were able to reproduce...
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Quantum mechanical study of the electron hopingp rocesses of heterocyclic molecules.Simulation of absorption and emission spectra.
Tichý, Ondřej ; Burda, Jaroslav (advisor) ; Profant, Václav (referee)
This thesis is about computing lifetimes of excited states of molecules by using semiempirical methods in simulations of molecular dynamics. Pyrimidine nucleobases and three aza- derivatives were chosen as reference molecules. Simulations of molecular dynamics by program MNDO99 were performed with these molecules and static spectra were computed by programs Gaussian and Orca. All the examined molecules have femtosecond lifetimes of second excited states, pyrimidine nucleobases have also short lifetimes of first excited states in hundreds of femtoseconds. The computed first excited states of aza-derivatives have lifetimes in tens or hundreds of picoseconds and suggest that the higher stability of the states is related to the smaller number of amino groups attached to the ring.
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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.
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Theoretical investigation of novel two-dimensional materials with application potential
Lyu, Pengbo ; Nachtigall, Petr (advisor) ; Maurin, Guillaume (referee) ; Straka, Michal (referee)
Electron confinement due to the two-dimensional (2D) nature of layered materials accounts for their fascinating electronic properties and for their applications in new-generation electronic devices. Moreover, the large specific surface area of 2D materials also enables their use in surface-related applications, such as catalysis and adsorption. In addition, these 2D materials are promising photocatalysts thanks to the shorter migration distance of photogenerated electrons and of electron holes. The research reported in this thesis aimed to provide atomistic insight into 2D layered materials, particularly into their structures, electronic properties and potential applications in the field of catalysis, photocatalysis and alkali metal ion batteries. Our findings are not only theoretically relevant but also open new research avenues for our experimental collaborators to improve specific properties and activities of their materials. The main results from this thesis, for five different classes of 2D materials, are summarized below. 2D covalent organic frameworks (COFs). CTF-type COFs with similar topology but different nitrogen-to-carbon ratios were investigated for their potential in photocatalytic water splitting. More specifically, torsion and bending effects on structure stability were investigated in...
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Theoretical Modeling of Two-dimensional Magnetic Materials
He, Junjie ; Nachtigall, Petr (advisor) ; Zhang, Gang (referee) ; Blonski, Piotr (referee)
Two dimensional (2D) materials, such as graphene, phosphorene and transition metal chalcogenides, have received a great attention in recent years due to their unique physical and chemical properties. A majority of 2D materials is intrinsically non-magnetic, therefore, their applications in spintronics are limited. The design and synthesis of new 2D materials with intrinsic magnetism and high spin-polarization remains a challenge. Computational discovery of new 2D materials with desired magnetic and electronic properties is the subject of this thesis. Using density functional theory with PBE, PBE+U and HSE06 functionals, we have systematically investigated the structure, electronic, magnetic and topological properties of novel 2D materials. Investigated materials include MXenes and layered transition-metal trihalides, both with great potential applications in spintronic devices. Four different classes of materials showing unique magnetic properties were investigated and reported in this thesis. (1) Asymmetrically functionalized MXenes were studied. The coexistence of the fully compensated antiferromagnetic order (zero magnetization) and completely spin-polarized semiconductivity was found for the first time. Moreover, the spin carrier orientation and induced transition from bipolar antiferromagnetic...
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Development and applications of molecular dynamics for molecular spectroscopy
Kessler, Jiří
This Thesis deals with simulations of chiroptical spectra using a combination of molecular dynamics and quantum chemistry. Molecular dynamics was used to explore conformational behaviour of studied systems (proteins), quantum chemistry for calculation of spectral prop- erties. The Quantum chemical methods are limited to relatively small systems. We overcome this problem mostly by a fragmentation of studied systems, when smaller, computationally feasible, fragments are created and used for the quantum chemical calculations. Calculated properties were then transferred to the big molecule. Vibrational Optical Activity (VOA) spectra of poly-L-glutamic acid fibrils (PLGA), insulin prefibrillar form and native globular proteins were studied. The simulated spectra provided satisfactory agreement with the experiment and were used for its interpretation. Experimental Vibrational Circular Dichroism (VCD) spectra of poly-L-glutamic acid fibrils were only qualitatively reproduced by the simulation. We could reproduce the major amide I band and a smaller negative band associated with the side chain carboxyl group. Our simulation procedure was then extended to a set of globular proteins and their Raman Optical Activity (ROA) spectra. Here we achieved an exceptional precision. For example, we were able to reproduce...
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