This thesis primarily focuses on various topics related to ferroelectric materials. Thesetopics include Landau-Ginzburg-Devonshire (LGD) theory for stable ferroelectricity in HfO2, the development of a molecular dynamics potential for ferroelectric alloys, the study of relaxor ferroelectrics for a stable dielectric response, and the investigation of terahertz enhanced lattice dynamics in a hybrid perovskite material. Due to its compatibility with silicon and stable ferroelectric response down to the thinnest films, HfO2 has attracted fundamental interest recently. It has been hypothesized that the stability of ferroelectricity in HfO2 arises from the phenomenon of improper ferroelectric, where the polarization is not the order parameter. In this scenario, there are other order parameters (typically zone boundary modes) that are not unaffected by the depolarization field. These order parameters would create a tri-linear coupling that shifts the stable polarization minima to some finite value. By contrast, our work suggests that the phase transition in HfO2 from tetragonal to orthorhombic ferroelectric phase is a two-step proper phase transition. The first step is an antiferroelectric phase transition, followed by a proper ferroelectric phase transition. The coupling of the antiferroelectric and ferroelectric order parameters results in an alternating polar and spacer structure, enabling stable ferroelectricity even under a depolarization field. Despite the successful explanation of this macroscopic symmetry change using the LGD model, The underlying atomistic details still require exploration. This necessitates finite-temperature and large-scale simulations such as classical molecular dynamics simulation. We proposed a ferroelectric alloy classical force field generating a schema for Ba1−xCaxZrO3 based on the bond-valence model. Our force field successfully reproduced experimentally observed static and dynamic responses, thereby confirming its high quality. Based on this force field, we validated the previous conjecture that inplane strain could induce a phase transition from a paraelectric to a ferroelectric state in the alloy material. Furthermore, we discovered that organizing cations into ordered by layer resulted in an antiferroelectric state for Ba0.5Ca0.5ZrO3, while random doping favors the paraelectric state. As doping becomes more complex with different chemical variants, the ferroelectric material exhibits a relaxor with a diffuse polar phase transition. We investigated the origin of flat dielectric response in BaCaTiO3 – Bi(Mg1/2Ti1/2)O3 alloy system. We found this material exhibits ultra-short-range correlations and nearly temperature-independent correlations, which are confined by chemical inhomogeneity. Furthermore, we uncovered the atomistic origins of the relaxor behavior. Finally, through a combined theoretical and experimental approach, we investigated the Raman response of two-dimensional hybrid perovskites (2DHP) for single-layered (n=1) and double-layered (n=2) cases. We found that A-site MA (MA=methylammonium) cations in (BA)2MAPb2Br7 (BA=butylammonium) for the n=2 case would result in a more diffusive Raman response. The absence of MA molecules in single-layered BA2PbBr4 (n=1) perovskite leads to its sharper Raman peak, thus resulting in stronger THz-induced lattice dynamics.