The first study project is based on modeling Earth abundant 3d transition-metal methoxide complexes with potentially redox-noninnocent ligands for methane C–H bond activation to form methanol (LnM-OMe + CH4 → LnM–Me + CH3OH). Three types of complex consisting of tridentate pincer terpyridine-like ligands, and different first-row transition metals (M = Ti, V, Cr, Mn, Fe, Co, Ni, and Cu) were modeled to elucidate the reaction mechanism as well as the effect of the metal identity on the thermodynamics and kinetics of a methane activation reaction. The calculations showed that the d electron count of the metal is a more significant factor than the metal's formal charge in controlling the thermodynamics and kinetics of C–H activation. These researches suggest that late 3d-metal methoxide complexes that favor σ-bond metathesis pathways for methane activation will yield lower barriers for C–H activation, and are more profitable catalyst for future studies. Second, subsequently, on the basis of the first project, density functional theory is used to analyze methane C−H activation by neutral and cationic nickel-methoxide complexes. This study identifies strategies to further lower the barriers for methane C−H activation through evaluation of supporting ligand modifications, solvent polarity, overall charge of complex, metal identity and counterion effects. Overall, neutral low coordinate complexes (e.g. bipyridine) are calculated to have lower activation barriers than the cationic complexes. For both neutral and cationic complexes, the methane C−H activation proceed via a σ-bond metathesis rather than an oxidative addition/reductive elimination pathway. Neutralizing the cationic catalyst models by a counterion, BF4-, has a considerable impact on reducing the methane activation barrier free energy. Third, theoretical studies were performed to explore the effects of appended s-block metal ion crown ethers upon the redox properties of nitridomanganese(V) salen complexes, [(salen)MnV(N)(Mn+-crown ether)]n+, where, M = Na+, K+, Ba2+, Sr2+ for 1Na, 1K, 1Ba, 1Sr complexes respectively; A = complex without Mn+-crown ether and B = without Mn+). The results of the calculations reveal that ΔGrxn(e ̶ ) and thus reduction potentials are quite sensitive to the point charge (q) of the s-block metal ions. Methane activation by A, 1K and 1Ba complexes proceeds via a hydrogen atom abstraction (HAA) pathway with reasonable barriers for all complexes with ~ 4 kcal/mol difference in energy, more favorable free energy barrier for the complexes with higher point charge of metal ion. Changes in predicted properties as a function of continuum solvent dielectric constant suggest that the primary effect of the appended s-block ion is via "through space" interactions. Finally, a comprehensive DFT study of the electrocatalytic oxidation of ammonia to dinitrogen by a ruthenium polypyridyl complex, [(tpy)(bpy)RuII(NH3)]2+ (complex a), and its NMe2-substituted derivative (b), is presented. The thermodynamics and kinetics of electron (ET) and proton transfer (PT) steps and transition states are calculated. NMe2 substitution on bpy reduces the ET steps on average 8 kcal/mol for complex b as compared to a. The calculations indicate that N–N formation occurs by ammonia nucleophilic attack/H-transfer via a nitrene intermediate, rather than a nitride intermediate. Comparison of the free energy profiles of Ru-b with its first-row Fe congener reveals that the thermodynamics are less favorable for the Fe-b model, especially for ET steps. The N-H bond dissociation free energies (BDFEs) for NH3 to form N2 show the following trend: Ru-b <Ru-a <Fe-b, indicating the lowest and most favorable BDFEs for Ru-b complex.

The overall objective of this thesis is to perform DFT based microscopic modeling of real cobaltates viewed as quantum spin liquid candidates and estimate their magnetic exchange parameters. Using the FPLO code with its Wannier function module, we estimated the onsite and intersite transfer integrals that are key quantities for a realistic material-specific description of the electron structure. Based on these results, theoretical approaches in the framework of hexagonal edge-sharing octahedra were applied to address the magnetic properties. We studied the three cobaltates Na2BaCo(PO4)2, Li3Co2SbO6 and Na3Co2SbO6 in detail. For each cobaltate that we calculated, we first examined the crystal structure. In the case of Na2 BaCo(PO4)2, we figured out uncertainties in the published crystal structure and investigated a plausible rotation of the O ligand octahedra, which we confirmed. For the two honeycomb cobaltates Li3Co2SbO6 and Na3Co2SbO6, we relaxed the crystal structure and numerically applied uniaxial strain along the c axis with the amount of ±0.05. We confirmed our suggestion that tensile strain brings the compressed octahedra closer to cubic symmetry. In the standard DFT approach with the GGA functional, we obtained wrong metallic behavior for insulating materials. This is a well-known shortcoming of the non-magnetic treatment and the insufficient account of the strong electron correlation. To overcome this issue, magnetic DFT+U calculations were performed. We were able to achieve excellent Wannier function fits on the calculated band structures for the two models: d and dp. The latter includes the O p states, which is reasonable because of the strong hybridization. For the honeycomb cobaltates Li3Co2SbO6 and Na3Co2SbO6 it was necessary to include the Sb 5s state located in the center of the hexagonal void to achieve such excellent Wannier function fits. With the help of the additional dp model, we can distinguish between different direct and indirect hopping processes. These Wannier function analyses give us the onsite properties and intersite processes which are the key quantities of the microscopic model and determine the magnetic behavior. The derived onsite properties of all three cobaltates are used to determine the crystal field parameters and the spin-orbit coupling constants by two methods: diagonalization and matrix comparison. In both methods, we achieved proper values for the cubic splitting, the charge transfer gap and the spin-orbit coupling constant. The sign of the trigonal splitting is at odds with the simple point charge model of the respective distorted octahedra. For Na2 BaCo(PO4)2 , we go a step further and use the crystal field parameters to calculate the multiplet energy levels and g-factors with ELISA. Compared with ESR measurements, we found that the results of the published structure are in a better agreement where the structure seems to be inaccurate. Evaluating the intersite hopping processes for all three cobaltates shows a good agreement with the cubic-symmetry-allowed hoppings. This reveals the closeness of the structures with honeycomb and cubic symmetry of the octahedra, respectively. The leading nearest neighbor process found for the z-bond is t3 between the two d_xy orbitals. The extended dp model allows for a resolution in direct and indirect hopping processes. We found that t3 in Na2BaCo(PO4)2 is dominated by indirect contributions, while in Li3Co2SbO6 and Na3Co2SbO6 the direct contributions dominate. One important outcome of this thesis is the sensitivity of hopping terms regarding structural modifications like optimization, relaxation or applying strain. Especially the honeycomb cobaltates Li3Co2SbO6 and Na3Co2SbO6 show high sensitivity on the crystal structure. Even small modifications by relaxing the crystal structure alter the hierarchy of the leading hoppings. Furthermore, the status quo between direct and indirect contributions can change dramatically. As the important 3rd neighbor hoppings in Li3Co2SbO6 and Na3Co2SbO6 are indirect, the major hopping paths were discovered. In the literature we found three different theoretical approaches to calculating the magnetic exchange parameters. With these and the onsite and intersite properties estimated before, we determined the magnetic exchange parameters in dependence on strain for Li3Co2SbO6 and Na3Co2SbO6. A direct comparison revealed that results for each approach are rather different. Hence, a universal theory model for these systems is still in development. With that we confirm the substantial controversy regarding the strength and the sign of the magnetic exchange terms. Following from the sensitivity of the hopping terms, the magnetic exchanges are also quite sensitive to modifications of the crystal structure. We located the cobaltates Li3Co2SbO6 and Na3Co2SbO6 in the phase diagram and found that they mainly occupy the zigzag-y phase also confirmed by experiments. Li3Co2SbO6 shows a promising behavior for increasing tensile strain: crossing the quantum spin liquid phase into the ferromagnetic phase. So the magnetic properties of Li3Co2SbO6 are more sensitive compared to Na3Co2SbO6 . The possibility of reaching the quantum spin liquid phase is theoretically given for Li3Co2SbO6 . With Li3Co2SbO6 covering the quantum spin liquid phase, the octahedra have almost the higher threefold rotational symmetry when checking the angles in the octahedra. In our investigations, we showed that real material simulations give valuable insights into the magnetic properties. Thereby Wannier function analyses are a powerful tool in the estimation of onsite and intersite terms. This makes several desired characteristics and parameters accessible and helps to link theory with experiment. In addition to that, we offered interesting insights into the microscopic behavior and trends when applying numerical strain on the crystals. This provides valuable hints for further research in this field.:List of figures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . III List of tables . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . VIII Acronyms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . XI 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 2. Material and methods . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 2.1. Magnetism of cobaltates . . . . . . . . . . . . . . . . . . . . . . . . . 3 2.1.1. One-electron Hamiltonian for l = 2 . . . . . . . . . . . . . . 4 2.1.2. Multiplets of the 3d shell . . . . . . . . . . . . . . . . . . . . . 10 2.2. Quantum spin liquids . . . . . . . . . . . . . . . . . . . . . . . . . . . 12 2.2.1. Kitaev honeycomb lattice model . . . . . . . . . . . . . . . 14 2.3. Slater-Koster terms in a honeycomb lattice . . . . . . . . . . 15 2.4. Density functional theory . . . . . . . . . . . . . . . . . . . . . . . . 20 2.4.1. Quantum mechanical many-body systems . . . . . . . 21 2.4.2. Hohenberg-Kohn theorems . . . . . . . . . . . . . . . . . . . 22 2.4.3. Exchange-correlation functional and Kohn-Sham equation . . 23 2.4.4. Wannier function projections . . . . . . . . . . . . . . . . . . 24 2.4.5. DFT+U for correlated insulators . . . . . . . . . . . . . . . . 25 2.5. Technical details of the calculations . . . . . . . . . . . . . . . . 26 2.5.1. Choice of the k-mesh . . . . . . . . . . . . . . . . . . . . . . . . 27 2.5.2. Cutoff parameter for WFs . . . . . . . . . . . . . . . . . . . . . 28 2.5.3. Relaxation routine . . . . . . . . . . . . . . . . . . . . . . . . . . . 28 3. The triangular-lattice cobaltate Na2BaCo(PO4 )2 . . . . . . . 30 3.1. Crystal structure and band structure . . . . . . . . . . . . . . . . 31 3.2. Structural optimization . . . . . . . . . . . . . . . . . . . . . . . . . . . 33 3.3. Wannier function analysis . . . . . . . . . . . . . . . . . . . . . . . . 35 3.3.1. Onsite properties . . . . . . . . . . . . . . . . . . . . . . . . . . . 38 3.3.2. Intersite processes . . . . . . . . . . . . . . . . . . . . . . . . . . 41 3.3.3. Magnetic exchange parameters . . . . . . . . . . . . . . . . 45 3.4. DFT+U calculations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 46 3.5. Summary and discussion . . . . . . . . . . . . . . . . . . . . . . . . 48 4. The honeycomb cobaltates Li3 Co2 SbO6 and Na3 Co2 SbO6 . . 50 4.1. Crystal structure and band structure . . . . . . . . . . . . . . . . 51 4.2. Structural optimization . . . . . . . . . . . . . . . . . . . . . . . . . . . 52 4.3. Application of uniaxial strain along the c-axis . . . . . . . . . . 54 4.4. Wannier function analysis . . . . . . . . . . . . . . . . . . . . . . . . . 58 4.4.1. Onsite properties . . . . . . . . . . . . . . . . . . . . . . . . . . . . 60 4.4.2. Intersite processes . . . . . . . . . . . . . . . . . . . . . . . . . . . 65 4.5. Magnetic exchange parameters . . . . . . . . . . . . . . . . . . . . 71 4.6. Summary and discussion . . . . . . . . . . . . . . . . . . . . . . . . . .75 5. Summary and outlook . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 77 A. Appendix . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 81 A.1. Details for the material and methods (Chapter 2) . . . . . . . 81 A.1.1. Cubic representation of the CF Hamiltonian . . . . . . . . . . 81 A.1.2. Derivation of the spin-orbit coupling Hamiltonian . . . . . . .82 A.2. Details for the triangular-lattice cobaltate Na2 BaCo(PO4)2 (Chapter 3) . . 86 A.2.1. DOS of DFT+U calculations . . . . . . . . . . . . . . . . . . . . . . . 86 A.2.2. Nearest neighbor hopping matrices for the y-bond . . . . . 86 A.2.3. Number of exchanges and systems of equations for the different magnetic configurations calculated with DFT+U . . . . . . . 87 A.3. Details for the honeycomb cobaltates (Chapter 4) . . . . . . . 90 A.3.1. Nearest neighbor hopping matrices for the y-bond . . . . . 90 Bibliography . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 92 Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 105

This thesis investigates the structural, energetic, and electronic properties of two-dimensional (2D) materials, focusing on graphene, hexagonal boron nitride (hBN), transition metal dichalcogenides (TMDCs), and arsenic phosphide (AsP) bilayers, using dispersion-corrected density functional theory (DFT) and random Phase Approximation (RPA). Central to our analysis is the use of dispersion-corrected DFT methods, particularly the SCAN-rVV10 and PBE-rVV10L functionals, to accurately predict interlayer distances, interaction energies, and electronic properties. We assess these properties across a wide range of 2D materials in both homogeneous and heterostructured forms. This thesis demonstrates the effectiveness of standard DFT methods in predicting intralayer properties like bond lengths and lattice constants. However, it is the advanced London dispersion-corrected functionals, such as SCAN-rVV10, that are particularly effective in detailing interlayer distances and interactions. These interlayer phenomena are crucial for accurate material characterization and application. For instance, in homogeneous and heterostructured layered systems, SCAN-rVV10 accurately predicts interlayer distances and interaction energetics, aligning closely with experimental and higher-level theoretical RPA results. Moreover, in studying binding behavior, particularly for {Mo,Ti}S2 nanostructures interacting with organic molecules, we illustrate how molecular orientation and surface structure influence binding characteristics. This research emphasizes that molecule interactions at edge and basal plane sites are crucial for controlling the shape and growth of these nanostructures. Molecules often bind more strongly to edge sites, promoting edge passivation and vertical stacking, while basal plane interactions, especially with thiophene, favor lateral growth. In conclusion, this thesis not only advances our understanding of the fundamental properties of 2D materials but also provides crucial insights into the accuracy of DFT methods in predicting these properties. By identifying the strengths and limitations of different dispersion-corrected DFT methods, we open the way for more accurate computational research and practical applications of these materials. This comprehensive analysis bridges theoretical predictions with potential industrial applications, underscoring the transformative impact of 2D materials in science and technology.

Magnetic ordering of dopants in diamond holds the prospect of exploiting diamond’s unique properties in the emerging field of spintronics. Several transition metal defects have been reported to order ferromagnetically in various semiconductors, however, low Curie temperatures and lack of other fundamental material properties have hindered practical implementation in room temperature spintronic applications. In this Thesis, we consider the energetic stability of 3d transition metal doped-diamond and its magnetic ordering properties at various lattice sites and charge states using ab initio Density Functional Theory methods. We find the majority of 3d transition metal impurities in diamond at any charge state to be energetically most stable at the divacancy site compared to substitutional or interstitial lattice sites, with the interstitial site being highly unstable (by ~8 - 10 eV compared to the divacancy site). At each lattice site and charge state, we find the formation energies of transition metals in the middle of the 3d series (Cr, Mn, Fe, Co, Ni) to be considerably lower compared to those early or late in the series. The energetic stability of transition metal impurities across the 3d series is shown to be strongly dependent on the position of the Fermi level in the diamond band gap, with the formation energies at any lattice site being lower in p-type or ntype diamond compared to intrinsic diamond. Further, we show that incorporation of isolated transition metal impurities into diamond introduces spin polarised impurity bands into the diamond band gap, while maintaining its semiconducting nature, with band gaps in both the spin-up and spin-down channels. These impurity bands are shown to originate mainly from s, p-d hybridization between carbon sp 3 orbitals with the 3d orbitals of the transition metal. In addition, the 4p orbitals contribute significantly to hybridization for transition metal atoms at the substitutional site, but not at the divacancy site. In both cases, the spin polarisation and magnetic stabilization energies are critically dependent on the lattice site and charge state of the transition metal impurity. By allowing magnetic interactions between transition metal atoms, we find that ferromagnetic ordering is likely to be achieved in divacancy Cr+2, Mn+2, Mn+1 and Co0 as well as in substitutional Fe+2 and Fe+1, indicating that transition metal-doped diamond is likely to form a diluted magnetic semiconductor which may successfully be considered for room temperature spintronic applications. In addition, these charge states correspond to p-type diamond, except for divacancy Co0, suggesting that co-doping with shallow acceptors such as B ( will result in an increase of charge concentration, which is likely to enhance mediation of ferromagnetic spin coupling. The highest magnetic stabilization energy occurs in substitutional Fe+1 (33.3 meV), which, also exhibits half metallic ferromagnetic ordering at the Fermi level, with an induced magnetic moment of 1.0 μB per ion, thus suggesting that 100 % spin polarisation may be achieved in Fe-doped diamond. / Physics / D. Litt. et Phil. (Physics)

I present detailed mechanistic analysis on the chemistry of glyoxylate as it pertains to forming biologically relevant molecules on the Hadean Earth. Chemistry covered includes: 1) the dimerization of glyoxylate to form dihydroxyfumarate(DHF), a heretofore unknown reaction, important to substantiating Eschenmoser's glyoxylate scenario. 2) Formation of sugars from polymerization of glyoxylate. 3) Formation of tartrate and sugar acids from high pH reactions of DHF. 4) Formation of glycine polypeptides from glyoxylate by transamination and coupling promoted by hexamethylenetetramine. 5) Formation of glyoxylate under conditions which could be plausibly found on the early earth.

The interplay between different self-organized electronically ordered states and their relation to unconventional electronic properties like superconductivity constitutes one of the most exciting challenges of modern condensed matter physics. In the present thesis this issue is thoroughly investigated for the prototypical layered material 1T-TaS2 both experimentally and theoretically. At first the static charge density wave order in 1T-TaS2 is investigated as a function of pressure and temperature by means of X-ray diffraction. These data indeed reveal that the superconductivity in this material coexists with an inhomogeneous charge density wave on a macroscopic scale in real space. This result is fundamentally different from a previously proposed separation of superconducting and insulating regions in real space. Furthermore, the X-ray diffraction data uncover the important role of interlayer correlations in 1T-TaS2. Based on the detailed insights into the charge density wave structure obtained by the X-ray diffraction experiments, density functional theory models are deduced in order to describe the electronic structure of 1T-TaS2 in the second part of this thesis. As opposed to most previous studies, these calculations take the three-dimensional character of the charge density wave into account. Indeed the electronic structure calculations uncover complex orbital textures, which are interwoven with the charge density wave order and cause dramatic differences in the electronic structure depending on the alignment of the orbitals between neighboring layers. Furthermore, it is demonstrated that these orbital-mediated effects provide a route to drive semiconductor-to-metal transitions with technologically pertinent gaps and on ultrafast timescales. These results are particularly relevant for the ongoing development of novel, miniaturized and ultrafast devices based on layered transition metal dichalcogenides. The discovery of orbital textures also helps to explain a number of long-standing puzzles concerning the electronic self-organization in 1T-TaS2 : the ultrafast response to optical excitations, the high sensitivity to pressure as well as a mysterious commensurate phase that is commonly thought to be a special phase a so-called “Mott phase” and that is not found in any other isostructural modification.

Organic and hybrid organic-inorganic photovoltaic (PV) devices have the potential to provide low-cost, large scale renewable energy. Despite the tremendous progress that has been made in this field, device efficiencies remain low. This low efficiency can be partly attributed to the low open-circuit voltages (Voc) generated by organic and hybrid organic-inorganic PV devices. The Voc is critically determined by the energy-level alignment at the interface between the materials forming the device. In this thesis we use first-principles methods to explore the energy-level alignment at the interfaces between the conjugated polymer poly(3-hexylthiophene) (P3HT) and three electron acceptors, zinc oxide (ZnO), gallium arsenide (GaAs) and graphene. We find that Voc reported in the literature for ZnO/P3HT devices is significantly lower than the theoretical maximum and that the interfacial electrostatic dipole plays an important role in the physics underlying the charge transfer at the heterojunction. We note significant charge transfer from the polymer to the semiconductor at GaAs/P3HT interfaces, and use this result to help interpret experimental data. Our findings support the conclusion that charge transferred from P3HT to GaAs nanowires can passivate the surface defect states of the latter and, as a result, account for the observed decrease in photoluminescence lifetimes. Finally, we explore the energy-level alignment at the graphene/P3HT interface and find that Voc reported for experimental devices is in line with the theoretical maximum. The effect of functionalised graphene is also examined, leading to the suggestion that functionalisation might have important consequences for device optimisation.

Heterogeneous electrocatalysis is the usage of solid materials to decrease the amount of energy needed to produce chemicals using electricity. It is of core importance for modern life, as it enables production of chemicals, such as chlorine gas and sodium chlorate, needed for e.g. materials and pharmaceuticals production. Furthermore, as the need to make a transition to usage of renewable energy sources is growing, the importance for electrocatalysis used for electrolytic production of clean fuels, such as hydrogen, is rising. In this thesis, work aimed at understanding and improving electrocatalysts used for these purposes is presented. A main part of the work has been focused on the selectivity between chlorine gas, or sodium chlorate formation, and parasitic oxygen evolution. An activation of anode surface Ti cations by nearby Ru cations is suggested as a reason for the high chlorine selectivity of the “dimensionally stable anode” (DSA), the standard anode used in industrial chlorine and sodium chlorate production. Furthermore, theoretical methods have been used to screen for dopants that can be used to improve the activity and selectivity of DSA, and several promising candidates have been found. Moreover, the connection between the rate of chlorate formation and the rate of parasitic oxygen evolution, as well as the possible catalytic effects of electrolyte contaminants on parasitic oxygen evolution in the chlorate process, have been studied experimentally. Additionally, the properties of a Co-doped DSA have been studied, and it is found that the doping makes the electrode more active for hydrogen evolution. Finally, the hydrogen evolution reaction on both RuO2 and the noble-metal-free electrocatalyst material MoS2 has been studied using a combination of experimental and theoretically calculated X-ray photoelectron chemical shifts. In this way, insight into structural changes accompanying hydrogen evolution on these materials is obtained. / Heterogen elektrokatalys innebär användningen av fasta material för att minska energimängden som krävs för produktion av kemikalier med hjälp av elektricitet. Heterogen elektrokatalys har en central roll i det moderna samhället, eftersom det möjliggör produktionen av kemikalier såsom klorgas och natriumklorat, som i sin tur används för produktion av t ex konstruktionsmaterial och läkemedel. Vikten av användning av elektrokatalys för produktion av förnybara bränslen, såsom vätgas, växer dessutom i takt med att en övergång till användning av förnybar energi blir allt nödvändigare. I denna avhandling presenteras arbete som utförts för att förstå och förbättra sådana elektrokatalysatorer. En stor del av arbetet har varit fokuserat på selektiviteten mellan klorgas och biprodukten syrgas i klor-alkali och kloratprocesserna. Inom ramen för detta arbete har teoretisk modellering av det dominerande anodmaterialet i dessa industriella processer, den så kallade “dimensionsstabila anoden” (DSA), använts för att föreslå en fundamental anledning till att detta material är speciellt klorselektivt. Vi föreslår att klorselektiviteten kan förklaras av en laddningsöverföring från ruteniumkatjoner i materialet till titankatjonerna i anodytan, vilket aktiverar titankatjonerna. Baserat på en bred studie av ett stort antal andra dopämnen föreslår vi dessutom vilka dopämnen som är bäst lämpade för produktion av aktiva och klorselektiva anoder. Med hjälp av experimentella studier föreslår vi dessutom en koppling mellan kloratbildning och oönskad syrgasbildning i kloratprocessen, och vidare har en bred studie av tänkbara elektrolytföroreningar utförts för att öka förståelsen för syrgasbildningen i denna process. Två studier relaterade till elektrokemisk vätgasproduktion har också gjorts. En experimentell studie av Co-dopad DSA har utförts, och detta elektrodmaterial visade sig vara mer aktivt för vätgasutveckling än en standard-DSA. Vidare har en kombination av experimentell och teoretisk röntgenfotoelektronspektroskopi använts för att öka förståelsen för strukturella förändringar som sker i RuO2 och i det ädelmetallfria elektrodmaterialet MoS2 under vätgasutveckling. / <p>QC 20151119</p>

Silicon nanowires (SiNWs) and the copper chalcogenides, namely copper sulfide (Cu2S) and selenide Cu2Se, have diverse applications in renewable energy technology. For example, SiNWs which have direct band gaps unlike bulk Si, have the potential to radically reduce the cost of Si based photovoltaic cells. However, they degrade quickly under ambient conditions. Various surface passivations have therefore been investigated for enhancing their stability but it is not yet well understood how they affect the electronic structure of SiNWs at a fundamental level. Here, we will explore, from first-principles simulation, how fluorine, methyl and hydrogen surface passivations alter the electronic structures of [111] and [110] SiNWs via strain and quantum confinement. We also show how electronic charge states in [111] and [110] SiNWs can be effectively modelled by simple quantum wells. In addition, we address the issue of why [111] SiNWs are less influenced by their surface passivation than [110] SiNWs. Like SiNWs, Cu2S and Cu2Se also make excellent photovoltaic cells. However, they are most well known for their exceptional thermoelectric performance. This is by virtue of their even more unique solid-liquid hybrid nature which combines the low thermal conductivity and good electrical characteristics required for a high thermoelectric efficiency. We use first-principles molecular dynamics simulations to show that Cu diffusion rates in Cu2S and Cu2Se can be as high as 10-5cm2s-1. We also relate their phonon power spectra to their low thermal conductivities. Furthermore, we evaluate the thermoelectric properties of Cu2S and Cu2Se using a combination of Boltzmann transport theory and first-principles electronic structure calculations. Our results show that both Cu2S and Cu2Se are capable of maintaining high Seebeck coefficients in excess of 200μVK-1 for hole concentrations as high as 3x1020cm-3.

A preconditioner to improve the convergence properties of Krylov subspace solvers is derived and analyzed in this work. This method is adapted to linear systems arising from a finite-element discretization of a phase-field crystal equation.