Browsing by Author "Kandemir, Zafer"

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Electronic struture of organic molecules containing transition-metal atoms
(Izmir Institute of Technology, 2019-07) Kandemir, Zafer; Bulut, Nejat
Hemoglobin including iron atom, vitamin B12 containing cobalt atom and ruthenium- based dye molecules are examples of organic molecules. We explore whether electron correlations arising from transition-metal atoms have any special role in the functioning of organic molecules using the effective multi-orbital Anderson model. We choose deoxy and oxy-heme molecules which are examples of hemoglobin derivatives because they have many experimental and theoretical studies. The experimental magnetic susceptibility measurements find that deoxy and oxy-heme molecules exhibit a high-spin to low-spin transition. We use four different computational methods: density functional theory (DFT), DFT+U, DFT+mean-field approximation (DFT+MFA) and DFT+quantum Monte Carlo (DFT+QMC) to study this transition. In this thesis, we compare the results of these methods with each other and the experimental results. DFT and DFT+U methods do not yield the high-spin state for deoxy-heme. DFT method correctly does not find the location of impurity bound state (IBS) known as correlated new electronic states. These methods obtain low-spin for oxy-heme, but they find that magnetic correlations are very small. DFT+MFA works well for high-spin, but this technique does not obtain low-spin because it does not find the location of IBS correctly. DFT+QMC gives the high(low)- spin state for deoxy-heme (oxy-heme) and finds IBS and magnetic correlations. We obtain that DFT+QMC works better among these methods for deoxy and oxy-heme molecules. Moreover, we investigate whether we can observe the IBS and magnetic correlations for vitamin B12, dye molecules and single-atom catalysts by using these computational approaches.
Mapping of the electronic structure of metalloproteins onto multi-orbital anderson model using the density functional theory
(Izmir Institute of Technology, 2013) Kandemir, Zafer; Bulut, Nejat
In this thesis, an effective Haldane-Anderson model is constructed in order to describe the electronic properties of a system where a the transition-metal impurity atom is added into a semiconductor host material. Metalloenzymes and metalloproteins are proteins which contain a transition metal. Vitamin B12 is a metalloenzyme which contains a cobalt (Co) atom. The vitamin B12 exhibits semiconducting properties due to the presence of a semiconductor gap in the electronic density of states. Thus, we argue that the electronic properties of vitamin B12 can be studied within the framework of the Haldane- Anderson model. In this thesis, firstly, the electronic structure of vitamin B12, which is known as cyanocobalamin, is obtained by using the Density Functional Theory (DFT) via the Gaussian program. By using the DFT results, the energies of the host and the 3d orbitals, and the hybridization terms between them are calculated. The final Haldane- Anderson Hamiltonian is obtained by adding the onsite Coulomb repulsion at the impurity 3d orbitals. The Haldane-Anderson Hamiltonian which has been constructed in this way from the DFT results can be studied by using the exact techniques many-body physics such as quantum Monte Carlo. Perturbative mean-field treats can also be used to study this Hamiltonian. Hence, the DFT calculations presented in this thesis represent the first step of thorough investigation of metalloproteins using these techniques of many-body physics.