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Nonlocal correlation in density functional theory
Hermann, Jan ; Bludský, Ota (advisor) ; Fišer, Jiří (referee)
e van der Waals (vdW) interactions, or dispersion forces, are crucial in many chem- ical, physical and biological processes and received much attention from developers of density functional theory (DFT) methods. e most popular non-empirical DFT method for treating vdW interactions is the vdW density functional by Dion et al. (vdW-DF). Despite its success, vdW-DF is not accurate enough for many chemical applications. Here, we investigate two possible ways how to improve its accuracy. First, we reoptimize the only weakly speci ed parameter of vdW-DF for several semi-local functionals. On the S benchmark database set, we nd that revPBE is the best performer, decreasing the error from . % to . %. Second, a system-speci c but very accurate (∼ . kcal/mol) DFT correction scheme is proposed for precise calcula- tions of adsorbent−adsorbate interactions by combining vdW-DF and the empirical DFT/CC correction scheme. e new approach is applied to small molecules (CH , CO , H , H O, N ) interacting with a quartz surface and a lamella of UTL zeolite. e very high accuracy of the new scheme and its relatively easy use and numerical stability compared to the earlier DFT/CC scheme o er a straightforward solution for obtaining reliable predictions of adsorption energies.
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Theoretical Investigation of silver clusters in zeolites
Hermann, Jan ; Nachtigall, Petr (advisor) ; Fišer, Jiří (referee)
The structure and stability of Agn+ 3 clusters (n = 1, 2, 3) in zeolite Y and their photochemical properties are investigated. Silver-exchanged zeolites have potential technological applications as UV-to-visible light converters. The structure and stability of silver clusters were examined using the periodic den- sity functional theory (DFT), and employing a developed and programmed geometry optimization driver. Non-reduced silver cations are preferably lo- cated in 6-member rings, far from each other. Upon a partial reduction, trigonal clusters are formed in the sodalite cages. The photochemical prop- erties are examined by various methods including the EOM-CCSD, MRPT2 and TD-DFT. No charge transfer transitions from ligands to silver clusters are found. Instead, transitions involving d and s electrons on silver clusters fall in the visible spectral range. Our results contradict the previous sugges- tion proposing existence of linear silver clusters through a double-6-member ring unit. Both parts of our investigations (structural and photochemical) disprove this previous proposition. A new interpretation of experimental spectra is proposed-the reduced trigonal silver cluster is responsible for photoactivity of Ag-doped zeolites with a low silver loading. Theoretical in- vestigation reported in this...
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Nonlocal correlation in density functional theory
Hermann, Jan ; Bludský, Ota (advisor) ; Fišer, Jiří (referee)
e van der Waals (vdW) interactions, or dispersion forces, are crucial in many chem- ical, physical and biological processes and received much attention from developers of density functional theory (DFT) methods. e most popular non-empirical DFT method for treating vdW interactions is the vdW density functional by Dion et al. (vdW-DF). Despite its success, vdW-DF is not accurate enough for many chemical applications. Here, we investigate two possible ways how to improve its accuracy. First, we reoptimize the only weakly speci ed parameter of vdW-DF for several semi-local functionals. On the S benchmark database set, we nd that revPBE is the best performer, decreasing the error from . % to . %. Second, a system-speci c but very accurate (∼ . kcal/mol) DFT correction scheme is proposed for precise calcula- tions of adsorbent−adsorbate interactions by combining vdW-DF and the empirical DFT/CC correction scheme. e new approach is applied to small molecules (CH , CO , H , H O, N ) interacting with a quartz surface and a lamella of UTL zeolite. e very high accuracy of the new scheme and its relatively easy use and numerical stability compared to the earlier DFT/CC scheme o er a straightforward solution for obtaining reliable predictions of adsorption energies.
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Assessment of dispersion corrected density functional methods.
Hermann, Jan ; Bludský, Ota (advisor) ; Nachtigallová, Dana (referee)
The problem of dispersion interaction in the DFT is reviewed, followed by a systematic study of the behaviour, in particular the transferability, of the LAP method. Dispersion is a kind of van der Waals forces, dominant in important molecular systems such as biomolecules or adsorption systems. The DFT is an ever increasingly used method for modelling chemical sys- tems. However, dispersion is rendered rather poorly in the DFT. We give an illustration of the problem and present some known correction methods. One of them is the local atomic potential (LAP) approach which we develop further from its original formulation, and this enables us to exactly match the benchmark interaction curves. We apply this development on systems consisting of benzene and a noble gas. We construct the LAPs for noble gas atoms and for carbon. It is shown that the LAP approach is poorly transfer- able based on our calculations. The investigation reported in this bachelor's thesis represents the rst attempt for an detailed study of the behaviour of the LAP method.
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Theoretical Investigation of silver clusters in zeolites
Hermann, Jan ; Nachtigall, Petr (advisor) ; Fišer, Jiří (referee)
The structure and stability of Agn+ 3 clusters (n = 1, 2, 3) in zeolite Y and their photochemical properties are investigated. Silver-exchanged zeolites have potential technological applications as UV-to-visible light converters. The structure and stability of silver clusters were examined using the periodic den- sity functional theory (DFT), and employing a developed and programmed geometry optimization driver. Non-reduced silver cations are preferably lo- cated in 6-member rings, far from each other. Upon a partial reduction, trigonal clusters are formed in the sodalite cages. The photochemical prop- erties are examined by various methods including the EOM-CCSD, MRPT2 and TD-DFT. No charge transfer transitions from ligands to silver clusters are found. Instead, transitions involving d and s electrons on silver clusters fall in the visible spectral range. Our results contradict the previous sugges- tion proposing existence of linear silver clusters through a double-6-member ring unit. Both parts of our investigations (structural and photochemical) disprove this previous proposition. A new interpretation of experimental spectra is proposed-the reduced trigonal silver cluster is responsible for photoactivity of Ag-doped zeolites with a low silver loading. Theoretical in- vestigation reported in this...
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