Point defects play a significant role in determining the physical and chemical properties of materials. Atomic-level simulation is a powerful tool to investigate and characterize the effect of these point defects. In this study, various aspect of the structure and stability of complex materials have been determined and predicted for lithium niobate, ceria-based systems, and titanium. The production, evolution, and dynamic behavior of defects have been explored. The focus has been on establishing the relationship between point defects and fundamental properties of bulk materials.;Lithium niobate is an important ferroelectric and non-linear optical material. For lithium niobate, the dominant defects with the lowest formation energies and their equilibrium structures are predicted under various experimental relevant environments. The site preferences with corresponding charge compensation mechanisms are compared with experimental observations. The diffusion mechanism and energy barrier are determined to elucidate the dynamic behavior of defect and defect clusters. The effects of point defects on the polarization of the system are also discussed.;Ceria-based systems are considered as potential electrolytes of solid oxide fuel cells. In ceria-based systems, the effects of sub-stoichiometry, temperature and ionic radii on the mechanical properties are evaluated using molecular dynamics simulation. It is observed that sub-stoichiometry lead to a significant softening of the elastic constants. Similar results are predicted for doped ceria systems. These softening effects arise from the significantly reduced strength of ionic interactions.;Titanium is a candidate material for cladding of fast nuclear reactor system due to its high corrosion resistance and excellent mechanical properties. In this study, cascade simulations are carried out to investigate its radiation resistance. The effect of a high-energy atom (primary knock-on atom) is simulated with various energies, positions and orientations. A high disordered region with a large number of point defects is observed during the initial phases of simulations (ballistic phase), followed by recombination of interstitials and vacancies (relaxation phase). The effects of primary knock-on atom energies on remnant defects are established. The orientation effects of primary knock-on atom and the effects of grain boundaries are also evaluated.