Electronic structure and correlations of vitamin B12 studied within the Haldane-Anderson impurity model

We study the electronic structure and correlations of vitamin B12 (cyanocobalamine) by using the framework of the multi-orbital single-impurity Haldane-Anderson model of a transition-metal impurity in a semiconductor host. The parameters of the effective Haldane-Anderson model are obtained within the Hartree-Fock (HF) approximation. The quantum Monte Carlo (QMC) technique is then used to calculate the one-electron and magnetic correlation functions of this effective model. We observe that new states form inside the semiconductor gap found by HF due to the intra-orbital Coulomb interaction at the impurity 3d orbitals. In particular, the lowest unoccupied states correspond to an impurity bound state, which consists of states from mainly the CN axial ligand and the corring ring as well as the Co e_g-like orbitals. We also observe that the Co(3d) orbitals can develop antiferromagnetic correlations with the surrounding atoms depending on the filling of the impurity bound states. In addition, we make comparisons of the HF+QMC data with the density functional theory calculations. We also discuss the photoabsorption spectrum of cyanocobalamine.Comment: 20 pages, 14 figure

Hemoglobinin biyolojik işlevindeki manyetik etki: Etkin çok orbitalli Anderson safsızlık modeli çerçevesinde DFT+QMC yaklaşımı

Thesis (Doctoral)--Izmir Institute of Technology, Materials Science and Engineering, Izmir, 2019Includes bibliographical references (leaves: 107-112)Text in English; Abstract: Turkish and EnglishHemoglobin corresponds to O2 transportation from lungs to the tissues and exhibits high-spin to low-spin transition by binding of O2 to Fe. In this thesis, we study the electronic and magnetic properties of the deoxy and the oxy forms of the human adult hemoglobin (HbA) to investigate the mechanism of the spin transition. We use an effective multi-orbital Anderson model and the parameters of this model are determined by the density functional theory (DFT) calculations. Then, this model is solved by using a quantum Monte Carlo (QMC) algorithm. The DFT+QMC results show that new electronic states named as the impurity bound states (IBS) exist in both deoxy-HbA and oxy-HbA.We also observe that as the temperature decreases, a magnetic gap is opened at the Fermi level for oxy-HbA. This gap arises from the Fe-O2 charge transfer. We find that both the IBS and the opening of the magnetic gap are responsible for the spin transition in hemoglobin. In addition, the DFT+QMC calculations show that antiferromagnetic (AF) correlations between the Fe(3d) and the surrounding orbitals exist in both deoxy-HbA and oxy-HbA. For deoxy-HbA, the anomalous magnetic circular dichrosim signal in the UV region is experimental evidence for these AF correlations. In the light of these magnetic measurements, we propose some explanations for the Bohr effect and the cooperativity which are the fundemental functional properties of the hemoglobin. The results presented in this thesis show that the magnetic effects play a crucial role in the funtioning of the hemoglobin.Hemoglobin molekülü, akciğerlerden hücrelere O2 taşınımından sorumludur ve O2'nin demire (Fe) bağlanmasıyla spin durumu yüksek-spinden düşük-spine geçmektedir. Bu tezde, deoksi ve oksi formdaki yetişkin insan hemoglobininin (HbA) elektronik ve manyetik özellikleri etkin çok-orbitalli Anderson modeli ile çalışılmıştır. Bu modelin parametreleri yoğunluk fonksiyoneli teoremi (DFT) ile elde edilmiştir. Daha sonra, kuantum Monte Carlo (QMC) algoritması ile bu model çözülmüştür. DFT+QMC sonuçları deoksi-HbA ve oksi-HbA moleküllerinde safsızlık bağıl durumu (IBS) olarak adlandırılan yeni elektronik hallerin var olduğunu göstermiştir. Ayrıca, sonuçlar, sıcaklık düştükçe, oxy-HbA için Fermi seviyesinde bir manyetik aralığın oluştuğunu göstermektedir. Bu manyetik alınganlık Fe-O2 yük geçişinden kaynaklanmaktadır. Bu tezde sunulan spin geçiş mekanizması hem IBS'lerin varlığının hem de manyetik aralığın açılmasının yüksek-spinden düşük-spine geçişe neden olduğunu göstermektedir. Buna ek olarak, deoksi-HbA ve oksi-HbA moleküllerinde Fe(3d) ile çevre orbitaller arasında antiferromanyetik (AF) korelasyonların var olduğunu bulduk. Deoksi-HbA için, UV bölgesindeki anomal manyetik dikroizm sinyallerinin bu AF korelasyonlar için deneysel bir kanıt olduğunu gösterdik. Bu manyetik ölçümler ışığında, hemoglobinin önemli fonksiyonel özellikleri olan Bohr etkisi ve kooperativite için açıklamalar önerdik. Bu tezde sunulan sonuçlar manyetik etkilerin hemoglobinin işleyişinde önemli rol oynadığını göstermektedir.TUBITAK (113F242

On party attachment in Western Europe and the utility of eurobarometer data

SIGLEUuStB Koeln(38)-890106740 / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekPreprintDEGerman

Magnetic mechanism for the biological functioning of hemoglobin

WOS: 000540510300072PubMed: 32444622The role of magnetism in the biological functioning of hemoglobin has been debated since its discovery by Pauling and Coryell in 1936. The hemoglobin molecule contains four heme groups each having a porphyrin layer with a Fe ion at the center. Here, we present combined density-functional theory and quantum Monte Carlo calculations for an effective model of Fe in a heme cluster. In comparison with these calculations, we analyze the experimental data on human adult hemoglobin (HbA) from the magnetic susceptibility, Mossbauer and magnetic circular dichroism (MCD) measurements. In both the deoxygenated (deoxy) and the oxygenated (oxy) cases, we show that local magnetic moments develop in the porphyrin layer with antiferromagnetic coupling to the Fe moment. Our calculations reproduce the magnetic susceptibility measurements on deoxy and oxy-HbA. For deoxy-HbA, we show that the anomalous MCD signal in the UV region is an experimental evidence for the presence of antiferromagnetic Fe-porphyrin correlations. The functional properties of hemoglobin such as the binding of O-2, the Bohr effect and the cooperativity are explained based on the magnetic correlations. This analysis suggests that magnetism could be involved in the functioning of hemoglobin

Corrosion modelling of spent fuel - adsorption of O, O2, H2O and H2O2 to the UO2 surface

International audienceCorrosion of nuclear fuel (UO2) leads to the formation of higher-order oxides up to U3O8. In order to study this oxidation, we investigate the adsorption of the O atom and oxygen-containing molecules (O2, H2O, H2O2) on the three most stable UO2 sur- faces ((111), (110), and (100)). The calculations are performed within DFT, using PBE+U including spin-orbit coupling and taking into account the non-collinear 3k (transverse) magnetic ground state.Dissociative adsorption is found for H2O and H2O2 on the (111) and (100) UO2 surfaces respectively, forming hydroxyl groups on the surface. Adsorption on the UO2 surface lowers the barrier to dissociation of O2. Defect formation energy is calculated for interstitial oxygen, up to several layers into the material starting from the surface. Diffusion energy barriers are presented. Adsorption energies are also studied as a function of temperature and partial pressure

Corrosion modeling of spent fuel – adsorption of O, O2, H2O and H2O2 on the UO2 surface

International audienceUranium dioxide (UO2) is the main component of nuclear fuels. This compound is very susceptible to oxidation, which results in the formation of the mixed-valence oxide U3O8. [1] From an application point of view, this interest relates to the safe and sustainable management of nuclear fuel. Our goal is an understanding of this oxidation process at the atomic level, using ab initio electronic structure calculations. The focus of this work lies in the early oxidation of stoichiometric UO2, where excess oxygen can be treated as interstitial point defects. In order to study this oxidation we investigate the adsorption of the O atom and oxygen-containing molecules (O2, H2O, H2O2) on the three most stable UO2 surfaces ((111), (110), and (100)). The calculations are performed within DFT, using PBE+U including spin-orbit coupling and taking into account the non-collinear 3k (transverse) magnetic ground state. Dissociative adsorption is found for H2O and H2O2 on the (111) and (100) UO2 surfaces respectively, forming hydroxyl groups on the surface. Adsorption on the UO2 surface lowers the barrier for the dissociation of O2. The defect formation energy is calculated for interstitial oxygen, up to several layers into the material starting from the surface. Additionally, adsorption energies are studied as a function of temperature and partial pressure