| Onsite screened Coulomb interaction plays an important role in determining the structural and electronic properties of strongly correlated materials, and Coulomb interaction of electrons in localized defect states controls the properties of deep centers. When studying the electronic structure in these systems, the Coulomb interaction between electrons is usually treated as adjustable parameters within model-Hamiltonian based approaches. This seriously compromises the predictive power of those theoretical methods.;We have developed a self-consistent first-principles approach to evaluating the screened Coulomb and exchange parameters using the constrained random phase approximation (cRPA). In the cRPA implementation of this thesis, the localized electrons are described in terms of the maximally localized Wannier functions and the dielectric screening is evaluated within the constrained RPA. We present a comprehensive study of the self-consistent cRPA approach and the calculated parameters for the 3d electrons in transition metals and transition metal oxides. We will also present preliminary results for localized defect systems. Quasiparticle calculations within the GW approximation are also discussed, and we present results for some of the materials mentioned above. |
