Interfaces in materials play a key role for industrial applications. The structures and dynamics at various interfaces including ferroelectric domain walls, gas-organic interface, organic-semiconductor interface and metal-gas interface are investigated with different atomic levels of simulation approaches. Ferroelectricity: Due to their unique ferroelectric and nonlinear optical properties, trigonal ferroelectrics such as LiNbO3 and LiTaO 3, are of wide interest for their potential applications in optoelectronics and nonlinear optics. The properties of these materials are heavily influenced by the shape of ferroelectric domains and domain walls. Therefore, investigation of the local structure and energetics of the ferroelectric domain walls and their interaction with defects on atomic scales, which is not clearly understood, is extremely important. The structure and energetics of ferroelectric domain walls in LiNbO 3 are examined using density functional theory (DFT) and molecular dynamics (MD) methods. The energetically favorable structures of 180° domain walls and the activation energy for domain wall motion are determined by atomic level simulations. The variation of polarization due to the presence of domain walls is also discussed. Defects can be pinned by domain walls. Various defects-domain walls interactions and the effects on domain wall motion are described using atomic level simulation methods. Although the structure of LiTaO3 is very similar with LiNbO3, it has been said experimentally that the shapes of domain walls are different with the presence of particular defects. Using both DFT and a newly developed interatomic potential for LiTaO 3, the differences in domain wall structure are understood in terms of the difference in energetics of domain walls between two materials. Polymerization: Surface polymerization by ion-assisted deposition (SPIAD) enables the control of thin film chemistry and morphology on the nanoscale during growth of conductive polymer thin films. This method allows fine tuning of optical band gaps and other optoelectronic properties of a polymer film by controlling the structure and kinetic energy of the depositing ions and neutrals. Thus, a comprehensive understanding of various mechanisms on the atomic level will contribute to optimizing growth conditions during SPIAD. SPIAD simulations are performed to study polymerization and crosslinking behavior of polythiophene molecules at the gas-organic interfaces using DFT-MD method. The growth processes for polythiophene molecules are studied by depositing thiophene molecules with 25 eV kinetic energy on terthiophene surface. The mechanism and various processes for polymerization and crosslinking of polythiophenes will be discussed. The changes in bond chemistry at the polythiophene molecules and at a PbS nanocrystalline quantum dot (organic-semiconductor interface) after a collision of C2H+ molecules with the substrate are also addressed. Surface diffusion: Surface diffusion is a key concept for understanding catalytic behavior at the surface. We develop a new code implementing adaptive kinetic Monte Carlo (AKMC) method with the dimer transition searching mechanism. The code is developed with a simple Lennard-Jones (LJ) potential. A test of dimer method is performed by using 2-dimensional testing potential. Results of surface diffusion processes of an Al adatom on Al (111) surface using AKMC method are presented.