Master Degree / Yüksek Lisans Tezleri
Permanent URI for this collectionhttps://hdl.handle.net/11147/3008
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Master Thesis Quantum Monte Carlo Study of the Multi-Orbital Anderson Model Including the Su(2) Invariant Hund's Coupling(Izmir Institute of Technology, 2018) Öztarhan, Gökhan; Bulut, NejatIn this study, an SU(2) invariant multi-orbital Anderson impurity model is discussed to obtain the electronic properties of metalloproteins. Metalloproteins are organic molecules containing transition metal atoms. They have important roles in the chemical reactions taking place in organisms. The electronic properties of metalloproteins can be modeled by an effective Anderson impurity model. The effective Anderson impurity model can be studied with the quantum Monte Carlo algorithm developed by Hirsch and Fye (1986). In the quantum Monte Carlo simulations of the Anderson impurity model so far, only the longitudinal component of the Hund’s coupling term which arises from the Coulomb interactions between the 3d orbitals is taken into account. Spin-flip and pairhopping terms (the transverse terms of the Hund’s coupling) are not considered. They are required to make the Hamiltonian SU(2) invariant, which is related to the spin rotations, so that the Hamiltonian is more realistic. The treatment of the transverse Hund’s coupling with the Hirsch-Fye algorithm has been difficult because of the problems encountered in the Trotter decomposition. Instead, a series expansion method was developed by Sakai et al. (2006). Here, we combine the Hirsch-Fye quantum Monte Carlo algorithm with the series expansion method to study the SU(2) invariant multi-orbital Anderson impurity model. Therefore, we present results from quantum Monte Carlo simulations with the new algorithm.Master Thesis Investigation of the Electronic Structure of the Ruthenium Dyes Used in Solar Cells by Combining Hartree-Fock Theory With the Quantum Monte Carlo Technique(Izmir Institute of Technology, 2015) Berkman, Irmak Çağlar; Bulut, NejatThe Haldane-Anderson model is constructed to describe the electronic properties of a system where a transition-metal impurity atom is added into a semiconductor host material. The electric and magnetic properties of the ruthenium-based dyes are investigated by using Haldane-Anderson model in this study. Because ruthenium-based dyes are semiconductor and ruthenium atom is a transition metal and its 4d orbitals are considered as impurities for dye molecules. Density Functional Theory (DFT) and Hartree-Fock Theory (HF) was used to obtain the Haldane-Anderson model parameters of the ruthenium-based dyes. Multi-orbital Hirsch-Fye Quantum Monte Carlo (HFQMC) algorithm was used to investigate effect of onsite Coulomb interactions of impurity 4d orbitals. Firstly, the Anderson model parameters are calculated by using Hartree-Fock and Density Functional Theory. After that, the occupation numbers of 4d orbitals and the all orbital occupancies of the dye molecules are obtained by using the Hirsch-Fye Quantum Monte Carlo algorithm and the magnetization of 4d orbitals are calculated. Finally, physical meaning of our results are discussed.Master Thesis Electronic Correlations in Metalloproteins: a Quantum Monte Carlo Study(Izmir Institute of Technology, 2013) Mayda, Selma; Bulut, NejatMetalloproteins are proteins that contain a metal atom. Some metalloproteins include a transition metal such as vitamin B12 (Co) and hemoglobin (Fe) and these structures show semiconducting properties. In this thesis, as an example of metalloproteins, vitamin B12 is studied and electronic and magnetic properties of Co 3d electrons are examined by the quantum Monte Carlo method (QMC). Since vitamin B12 contains a cobalt (Co) atom and has a semiconductor gap, its electronic and magnetic properties can be described by multi-orbital Haldane-Anderson model. Haldane-Anderson model explains the electronic properties of semiconductors which contain a transition metal impurity and considers the onsite Coulomb interactions of impurity 3d orbitals. To solve this model, we use Hirsch-Fye quantum Monte Carlo algorithm (HFQMC) without making any approximations. Firstly, the occupations and intra-orbital electronic correlations of 3d orbitals are calculated. After that, the total magnetization and the inter-orbital correlations of 3d orbitals are obtained. Next, the total magnetic susceptibility and magnetic susceptibilities between the 3d orbitals are calculated. Finally, we discuss the physical meaning of the QMC calculations.