This thesis work was performed at AB Sandvik Coromant and aimed to enhance the knowledge about the relationships between the performance of TiN and TiAlN-coated cutting tools in metal turning and their mechanical and chemical properties. Measurements of coating material properties and turning wear tests in annealed tool steel Sverker 21, stainless steel 316L, grey cast iron V314 and nodular cast iron SS0727 were performed. The cutting temperatures were estimated from FEM-simulations. To find the dominant wear mechanism and identify the properties that are most important for the resistance against that particular wear, a correlation analysis was performed together with a wear study using LOM, SEM and EDS. The results show that relations between cutting performance and mechanical properties and/or composition of the coatings can be established. The FEM-simulations suggested that the peak tool temperature was highest, ~750°C, for turning in 316L and lowest for turning in Sverker 21, ~300°C. Turning in cast iron resulted in temperatures around 500-550°C. A mechanism for the growth of the crater on inserts tested in stainless steel 316L is proposed. Wear due to thermo-mechanical load and adhesion are believed to be the dominating wear mechanisms. The performance of the tool showed a high correlation to the composition of the coatings, with a decreased tool life for higher Al-contents. The reason for this might lie in an increased brittleness of these coatings, accelerating formation of lateral cracks above the crater. Calculated ratios of bulk and shear modulus suggests an increased brittleness for higher Al-contents. A higher tendency to stick to the work piece material might also contribute to a decrease in tool life. An Increased Al-content could also drive the formation of c-AlN to h-AlN, causing even higher wear rates. The coatings with higher substrate bias showed an enhanced performance, even though the crack pattern was worsened for these variants. The reason for the enhanced performance seen for these variants might instead originate in an enhanced adhesion to the substrate. In the flank wear resistance test in Sverker 21 the Al-content proved to be important, with an improved performance for higher Al-contents. In contrast to the test in 316L, a change in bias or hardness had no effect on the performance in this test. Scratch patterns on the flank supports that an abrasive wear mechanism is present, but no correlation between hardness and tool life could be obtained. Either some other material property than hardness is of importance for the abrasive resistance in this test, or another wear mechanism, occurring simultaneously with abrasion, is the wear rate deciding. The second part of this thesis work was to evaluate the ability of a quantum mechanical computational method, density functional theory, to predict material properties. The method predicts the lattice parameters and bulk moduli in excellent agreement with experimental values. The method also well predicts other elastic properties, with results consistent with reference values. There seems to be a constant shift of about 50-100 GPa between the calculated elastic modulus and the experimentally measured values, probably originating in contributions from grain boundaries, texture, stresses and defects present in the real coatings, and possibly also in errors in the experimental method due to an influence from the substrate. The calculated hardness values did not follow the trend of an increased hardness for TiAlN compared to TiN, which is seen in experiments.

In this thesis, a number of clean-energy materials for hydrogen generation, hydrogen storage, and Li-ion battery energy storage applications have been investigated through state-of-the-art density functional theory. As an alternative fuel, hydrogen has been regarded as one of the promising clean energies with the advantage of abundance (generated through water splitting) and pollution-free emission if used in fuel cell systems. However, some key problems such as finding efficient ways to produce and store hydrogen have been hindering the realization of the hydrogen economy. Here from the scientific perspective, various materials including the nanostructures and the bulk hydrides have been examined in terms of their crystal and electronic structures, energetics, and different properties for hydrogen generation or hydrogen storage applications. In the study of chemisorbed graphene-based nanostructures, the N, O-N and N-N decorated ones are designed to work as promising electron mediators in Z-scheme photocatalytic hydrogen production. Graphene nanofibres (especially the helical type) are found to be good catalysts for hydrogen desorption from NaAlH4. The milestone nanomaterial, C60, is found to be able to significantly improve the hydrogen release from the (LiH+NH3) mixture. In addition, the energetics analysis of hydrazine borane and its derivative solid have revealed the underlying reasons for their excellent hydrogen storage properties.  As the other technical trend of replacing fossil fuels in electrical vehicles, the Li-ion battery technology for energy storage depends greatly on the development of electrode materials. In this thesis, the pure NiTiH and its various metal-doped hydrides have been studied as Li-ion battery anode materials. The Li-doped NiTiH is found to be the best candidate and the Fe, Mn, or Cr-doped material follows. / <p>QC 20130925</p>

<p>The computational success of density functional theory relies on the construction of suitable approximations to the exchange-correlation energy functional. Use of functional approximations depending explicitly upon the density alone appear unable to address all aspects of many-body interactions, such as the fundamental constraint that the ground state energy is a piecewise linear function of the total number of electrons, and the ability to model nonlocal effects. Functionals depending explicitly upon occupied and unoccupied Kohn–Sham orbitals are considered necessary to address these and other issues. This dissertation considers certain issues relevant to the successful implementation of explicitly orbital-dependent functionals through the optimized effective potential (OEP) approach, as well as extending the potential functional formalism that provides the formal basis for the OEP approach to systems in the presence of noncollinear magnetic fields.</p><p>The self-consistent implementation of orbital-dependent energy functionals is correctly done through the optimized effective potential approach—minimization of the ground state energy with respect to the Kohn–Sham potential that generates the set of orbitals employed in the energy evaluation. The focus on the potential can be problematic in finite basis set approaches as determining the exchange-correlation potential in this manner is an inverse problem which, depending upon the combination of orbital and potential basis sets employed, is often ill-posed. The ill-posed nature manifests itself as nonphysical exchange-correlation potentials and total energies. We address the problem of determining meaningful exchange-correlation potentials for arbitrary combinations of orbital and potential basis sets through an L-curve regularization approach based on biasing towards smooth potentials in the energy minimization. This approach generates physically reasonable potentials for any combination of basis sets as shown by comparisons with grid-based OEP calculations on atoms, and through direct comparison with DFT calculations employing functionals not depending on orbitals for which OEP can also be performed. This work ensures that the OEP methodology can be considered a viable many-body computational methodology.</p><p>A separate issue of our OEP implementation is that it can suffer from a lack of size-extensivity—the total energy of a system of infinitely separated monomers may not scale linearly with the total number of monomers depending upon how we construct the Kohn–Sham potential. Typically, a fixed reference potential is employed to aid in the convergence of a finite basis set expansion of the Kohn–Sham potential. This reference potential can be utilized to ensure other desirable properties of the resulting potential. In particular, it can enforce the correct asymptotic behavior. The Fermi–Amaldi potential is often used for this purpose but suffers from size-nonextensivity owing to the explicit dependence of the potential on the total number of electrons. This error is examined and shown to be rather small and rapidly approaches a limiting linear behavior. A size-extensive reference potential with the correct asymptotic behavior is suggested and examined.</p><p>We also consider a formal aspect of the potential-based approach that provides the underlying justification of the OEP methodology. The potential functional formalism of Yang, Ayers, and Wu is extended to include systems in the presence of noncollinear magnetic fields. In doing so, a solution to the nonuniqueness issue associated with mapping between potentials and wave functions in such systems is provided, and a computational implementation of the OEP in noncollinear systems is suggested.</p><p>Finally, as an example of an issue for which orbital-dependent functionals seem necessary to obtain a correct description, we consider the ground state structures of C_{4<italic>N</italic> + 2} rings which are believed to exhibit a geometric transition from angle-alternation (<italic>N</italic> ≤ 2) to bond-alternation (<italic>N</italic> > 2). So far, no published DFT approach has been able to reproduce this behavior owing to the tendency of common density functional approximations to bias towards delocalized electron densities. Calculations are presented with the rCAM-B3LYP exchange-correlation functional that correctly predict the structural evolution of this system. This is rationalized in terms of the recently proposed delocalization error for which rCAM-B3LYP explicitly attempts to address.</p> / Dissertation

In this study, we used the Density functional theory (DFT) to obtain the relationship between mechanical property and electronic property of Boron nitride nanotubes (BNNTs) under the uni-axial strain. Moreover, we also investigated one CO molecule adsorbed on the BNNTs under the uni-axial strain. We also use the molecular dynamics to introduce the mechanical property and dynamic behavior of (8,8)BNNT under the uni-axial strain. There were three parts in this study: The first part: The effect of uni-axial strain on the electronic properties of (5,5) and (8,0)boron nitride nanotubes were obtained by DFT calculation. We used the HOMO-LUMO Gap¡Bbond angle¡Bbond length and radial buckling to analyze the electronic properties and mechanical properties. The stress-strain profiles indicated that different BNNTs types displayed very similar mechanical properties, but there were variations in HOMO-LUMO gaps at different strains, indicating that the electronic properties of BNNTs not only depend on uni-axial strain, but on BNNT type. In addition, the variations in nanotube geometries, partial density of states (PDOS) and charges of boron and nitride atoms were also discussed for (8,0) and (5,5) BNNTs at different strains. The second part: The DFT was used to investigate electronic properties of CO molecule adsorbed on BNNT under the uni-axial strain. The stress-strain profiles indicated that the CO molecule adsorption on BNNT leaded only to a local mechanical deformation. The strength of BNNT could not be affected when the CO molecule adsorbed on that. Moreover, we obtained that the charge of CO will slightly transfer to the adsorbed atom of BNNT when strain increased. Hence, the adsorption energy increased slightly under the uni-axial strain. The third part: The molecular dynamics simulations were performed to investigate deformation behaviors of (8,8)BN nanotubes under axial tensile strains at 300k. Variations with the tensile strain in the axial stress, bond lengths, bond angles, radial buckling, and slip vectors were all examined. The axial, radial, and tangential components of the slip vector were also employed to monitor, respectively, the local elongation, necking, and twisting deformation near the failure of the nanotube. The components of the slip vector grew rapidly and abruptly after the failure strain, especially for the axial component. This implies that the local elongation dominates the failure of the loaded BN nanotube and finally results in a chain-like tensile failure mode.

In this study, we employed density functional theory (DFT) and molecular dynamics (MD) to investigate the mechanical and electronic properties of one-dimensional zinc oxide nanostructure. This study can be arranged into two parts: In part I: We investigated the mechanical and electronic properties of one-dimensional zinc oxide nanostructure under axial mechanical deformations by density functional theory. In this case, we could find both the highest occupied molecular orbital and the lowest unoccupied molecular orbital gap (HOMO-LUMO gap) and value of radial buckling will decrease linearly with the increase of axial strain. The changes of bond lengths and bond angles show the variation of nanostructure dependence to the increase of axial strain. This study also used partial density of state (PDOS), bond order (BO) and deformation density to analyse the differences of the electronic properties between the zinc oxide nanotubes under axial strain. In part II: This study, which employed molecular dynamics combines Buckingham and Core-Shell potentials, shows the different physical parameters, such as yield stress, young¡¦s modulus and slip vector to research the mechanical behavior and variation of structure of nanotube under axial strain.

The structural and electronic properties of small tungsten nanoparticles Wn (n=2-16) were investigated by density functional theory (DFT) calculation. For the W10 nanoparticle, ten lowest-energy structures were first obtained by basin-hopping method (BH) and ten by big-bang method (BB) with the tight-binding many-body potential for bulk tungsten material. These fifty structures were further optimized by the DFT calculation in order to find the better parameters of tight-binding potential adquately for W nanoparticles. With these modified parameters of tight-binding potentials, several lowest-energy W nanoparticles of different sizes can be obtained by BH and BB methods and then further refined by DFT calculation. According to the values of binding energy and second-order energy difference, it reveals that the structure W12 has a relatively higher stability than those of other sizes. The vertical ionization potential (VIP), adiabatic electron affinity (AEA) and HOMO-LUMO Gap are also discussed for W nanoparticles of different sizes.

In this study, we used the molecular statics, molecular dynamics, and density function theory to investigate structural, electronic, and mechanical properties of ultra-thin silica nanowires. There are two parts in this study. In the first part, we used basin-hopping method to get different diameters of silica nanowires, nemed 2MR, 2MR-2O, 3MR-3O, 4MR-4O, 5MR-5O, 4MR-3f, 4MR-4f, and 4MR-5f. The various silica nanowires were optimized by density function theory to obtain the projected density of states, Mulliken charge, and electronic density difference, and we also compared this results to £\-quartz. In the second part, the molecular dynamics simulations were performed to investigate deformation behavior of silica nanowires under axial tensile loading at 10K. The Young¡¦s modulus increases when the diameter decreases. We also used angular correlation function to study the mechanical properties and variation of structures.

In this study, we used the Density functional theory (DFT) and Molecular dynamics (MD) to obtain the suitable hydrogen storage structure of Rh nanoclusters on the boron nitride sheet and Li atoms on the graphene. The reason of studying two type of nanoparticles is that there are two adsorption method in hydrogen storage, such as the adsorption of hydrogen molecules and hydrogen atoms. Using Rh nanoclusters on the boron nitride sheet to store hydrogen belong to the adsorption of hydrogen atoms. Using Li atoms on the graphene to store hydrogen belong to the adsorption of hydrogen molecules. We use these two models to simulate the hydrogen storage in this study. There were four parts in this study: The first part: The Density functional theory is utilized to obtain the configuration and corresponding energy of Rh nanoclusters, boron nitride sheet, Rh nanoclusters adsorbed on the boron nitride sheet, Li atoms adsorbed on the graphene, hydrogen adsorbed on the graphene and hydrogen adsorbed on the Li atoms. Then, we use the Force-matching method (FMM) to modify the parameters of potential function by the reference data which are obtained by Density functional theory. Finally, we use the modified parameters of potential function to perform Molecular dynamics in this study. The second part: In this part, the dynamical behavior of Rh nanoclusters with different sizes on the boron nitride sheet are investigated in temperature-rise period. The migration trajectory, square displacement and mean square displacement of the mass center of the Rh nanoclusters are used to analyze the dynamics behavior of Rh nanoclusters on the boron nitride sheet. The third part: In this part, the pristine graphene and graphen with Li atoms are investigated the efficiency of hydrogen storage at different temperature and pressure. In order to obtain the temperature (77K and 300K) and pressure effect of hydrogen storage, the densimetric distribution and gravimetric capacity (wt%) are analyzed. The fourth part: The Molecular dynamics is utilized to study the hydrogen storage and delivery when the distance between two graphene is different. Then, the temperature effect (77K and 300K) of hydrogen storage, the gravimetric capacity (wt%) are analyzed. In addition, the gravimetric capacity (wt%) of hydrogen delivery are also analyzed in the larger system space at 300K.

In this study, the structures of two ultrathin Pd nanowires were predicted by the simulated annealing basin-hopping method (SABH) with the tight-binding potential. The thermal stability of the Pd wires and adsorption, dissociation and diffusion behaviors were further examined by the density functional theory (DFT) calculation and DFT molecular dynamics (DFT-MD) simulation. In terms of thermal stability, these two Pd nanowires are still very stable at temperatures as high as 400 K. The configurations and adsorption energy have been calculated for H atom and H2 molecular adsorption on Pd nanowires. The minimum energy pathways and transition states of H2 molecular dissociation and H atom diffusion process on Pd nanowires were studied by the nudged elastic band (NEB) method. For the dissociation of hydrogen molecules, results show the dissociation is almost barrierless so the dissociation is easy to occur at very low temperatures, and their catalytic reactivity is very similar to the Pd bulk material. The thermal stability of the H atom within these Pd nanowires were also investigated by DFT-MD, with results showing that the H atom can only stay within Pd nanowires at temperatures much lower than room temperature (298 K). This phenomenon is very different from that of H atoms within Pd bulk material or other reported nanomaterials, leading to hydrogen embrittlement. Our results reveal that these two ultrathin Pd nanowires not only possess the same excellent catalytic activity for hydrogen molecules as the bulk Pd materials or other Pd nanomaterials do, but also avoid the hydrogen embrittlement occur.

The results from density functional theory (DFT) studies into C–H bond activation, hydrogen transfer, and alkyne–to–vinylidene isomerization are presented in this work. The reaction mechanism for the reductive elimination (RE) of methane from [ κ3- TpPtIV(CH3)2H (1)] (Tp = hydridotris(pyrazolyl)borate) by oxidative addition (OA) of benzene to form [ κ3-TpPtIV(Ph)2H] (19) was investigated through DFT calculations. For 31 density functionals, the calculated values for the barriers to methane formation (Ba1) and release (Ba2) from 1 were benchmarked against the experimentally reported values of 26 (Ba1) and 35 (Ba2) kcal•mol-1, respectively. The values for Ba1 and Ba2, calculated at the B3LYP/DZP level of theory, are 24.6 and 34.3 kcal•mol-1, respectively. The best performing functional was BPW91 where the m.a.e. for the calculated values of the two barriers is 0.68 kcal•mol-1. Classic and newly proposed mechanisms for metal-mediated hydrogen transfer (HT) were analyzed with density functional theory (DFT) and Bader's "Atoms In Molecules" (AIM) analysis. Seven sets of bonding patterns that characterize theconnectivity in metal-mediate HT were found from the analysis of representative models for σ-bond metathesis ( σBM), oxidative addition / reductive elimination (OA/RE), and alternative mechanisms. The mechanism for the formation of the alkynyl, vinylidene complex, [(PiPr3)2Rh(CCPh)(CC(H)(Ph))] (2), by the addition of two equivalents of phenylacetylene (PA) to [( η3-C3H5)Rh(PiPr3)2] (1) was studied through DFT calculations. Two experimentally observed intermediates on the reaction coordinate are the η2-PA, alkynyl complex, [(PiPr3)2Rh( η2-HCCPh)(CCPh)] (Ia) and the fivecoordinate, pseudo square-pyramidal, RhIII–H complex, [(PiPr3)2Rh(H)(CCPh)2] (Ib), and were found to be in equilibrium. The relative energies of Ia, Ib, and 2 (relative to 1 + 2PA) depend on the phosphine that was used in the calculation; the predicted product is 2 with PiPr3 and PEt3 but Ia with PMe3, PMe2Ph, PMePh2, PPh3, and PH3. The equilibrium between Ia and Ib was calculated with PEt3 and one conformation of PiPr3. We investigated the mechanism for the formation of 2 from Ia, and a lower energy pathway where the π-bound PA of Ia slips to bind through the σ-C–H bond prior to the formation of 2 through hydrogen migration was found.