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Transition metal nanoclusters have attracted a significant attention in both theoretical and experimental studies due to their unique properties such as structural, electronic and magnetic. These properties are distinct, size dependent and ranges between those of bulk and single-particle species. Some of the systems sizes have been experimentally synthesized, which enables direct theory-experiment comparison. Other clusters that have been examined theoretically are of interest as models of larger systems. Often, the size dependence of their HOMO-LUMO (H-L) gap, optical properties, magnetic properties, etc., is of interest. In this study, we have performed a genetic algorithm search on the tight-binding interatomic potential energy surface (PES) for small TiN (N = 2–32) clusters. Lowest energy candidate clusters were further refined using density functional theory (DFT) calculations with the PBEsol exchange-correlation functional and evaluated with the PBEsol0 hybrid functional. The resulting clusters were analysed in terms of their structural features, growth mechanism and surface area. The results suggest a growth mechanism that is based on forming coordination centres by interpenetrating icosahedra, icositetrahedra and Frank–Kasper polyhedra. We identified centres of coordination, which act as centres of bulk nucleation in medium-sized clusters and determine the morphological features of the cluster. Molecular dynamics simulations were performed in order to investigate the impact of thermal agitation on the TiN (N = 7, 13, 17, 32, 57, 80 and 89). The calculations were carried out at 300 – 2400 K. The interatomic interactions for vacuum and inert gas environment were modelled using Gupta and Leonard-Jones potentials as implemented within the classical molecular dynamics simulation software DL_POLY. The total potential energy, radial distribution functions (RDF), diffusion coefficient, mean square displacement and density profiles were examined to study the structur, University of Limpopo (UL) University College London (UCL) Royal Society Newton’s Grant (NA140447) National Research Foundation (NRF) Titanium Centre of Competence (TiCoC)

In this work, we present first-principles calculation on the structural, thermodynamic, mechanical and electronic stabilities of Fe-Al and FeAl-X (X: Pt, Pd, Ru and Ag) alloys at lower and high temperatures. These systems have recently attracted a lot of attention for both scientific and possible technological application in turbines, Steel-It coating, energy sector, boilers, pipes and automotive parts as a potential replacement of steel due to their excellent resistance to oxidation at high temperatures. However, they suffer limited room temperature ductility and a sharp drop in strength above 873 K. We determined the lattice parameters, heats of formation, elastic constants, bulk to shear moduli, density of states, phonon dispersion curve and X-ray diffraction pattern for binary and ternary system at various concentrations between 0 ≤ x ≤ 10. Furthermore, the lattice expansion, elastic constants, Gibbs free energy, X-ray diffraction pattern and radial distribution function were done on the most stable systems to determine the melting point of FeAl-X ternary systems. A systematic investigation was performed on the stability of the Fe-Al alloys at zero K. We employed CASTEP code to evaluate the thermodynamic, elastic and electronic stability. Virtual crystal approximation was used to determine various atomic concentrations (0 ≤ x ≤ 5) of both Pt and Ru; this allowed more precise predictions on the materials’ behaviour. Further analysis was done on the density of states to describe the behaviour of each phase near the Fermi level; these phases were observed at different percentage compositions. A supercell approach, DMol3 was also used to evaluate these systems at a larger scale (0 ≤ x ≤ 50). VASP and LAMMPS codes were used to determine the stability of these FeAl-X ternary systems at concentrations (0 ≤ x ≤ 10). It was found that the equilibrium lattice parameters of the binary systems are in good agreement to within 2% with the available experimental data. The heat

Calculations were carried out on transition-metal sulphides (TMS) and transitionmetal arsenides (TMA), in both pyrite- and marcasite-type structures, using planewave (PW) pseudopotential methods within density functional theory (DFT) in the local density approximation (LDA). The structural, electronic and optical properties for both pyrite- and marcasite-type structures (naturally occurring and converted) have been investigated. The equilibrium lattice parameters were investigated and are in good agreement with the experimental values. The heats of formation calculations predict that the naturally occurring pyrite- and marcasite-type structures are more stable than the converted ones. In particular, the calculated pyrite-type RuS2 compares well to the experimental value (with energy difference of 0.381 eV/atom). The bulk modulus and elastic properties were calculated. The predicted anisotropic ratio shows that the naturally occurring pyrite- and marcasite-type structures are more stable than the converted ones. Moreover, the electronic density of states and band structure calculations reveal that most compositions shows semiconducting behaviour except for the converted pyritetype structures, i.e OsAs2 and RuAs2 where a metallic behaviour was observed. The electronic charge density and charge density difference show charge accumulation on bonding atoms, predicting the charge gain/ loss and nature of bonding to be covalent/ weak ionic between the atoms. Lastly, optical properties are computed at equilibrium and predict that naturally occurring structures have lower absorption and reflectivity than the converted structures. At different pressures ranging from -10 GPa to 10 GPa, the absorption and reflectivity spectra show a shift from the 0 GPa spectrum for all the structures, National Research Foundation

The structural and energetic properties of the Ti-Al and Pt-Ti alloys have been carried out using first-principles total energy calculation of the density functional theory. We found a good correlation between VASP and CASTEP calculations with the experimental data. The equilibrium lattice constants for both systems are in good agreement with the experimental values (within 3% agreement). Furthermore, the heats of formation were calculated in order to determine the relative structural stabilities of the Ti-Al and Pt-Ti alloys. We predict that the L10 TiAl is the most stable structure with the lowest heats of formation (more negative Hf) consistent with the experimental observations. The 50% composition of the PtTi SMA’s in particular B19/B19′ phases predict values to be closer to each other, with B19′ being the most stable phase. A comparison of the energy differences between different PtTi phases, yields the relative energies in the order B2>L10>B19>B19'. The elastic constants for B19/B19′ and L10 show the positive shear modulus while a negative shear modulus was observed for B2 phase (mechanical instability). Similarly, the phonon dispersions and the density of states for the B2, L10, B19 and B19′ PtTi shape memory alloys were calculated and are consistent with the heats of formation. The phonon dispersion curves revealed a softening of modes along high symmetry directions (M and R). This confirms that the B2 structure is less stable as compared to the other structures. The density of states for the 50% PtTi composition structures were also calculated and are consistent with the stability trend. Furthermore the transformation from B2-L10 was investigated using Bain’s path and the B2 and L10 phases were depicted at c/a=1 and c/a=√2 respectively., NRF & CSIR