Abstract : Under this research grant, we carried out realistic first-principles computer calculations of the ground-state and finite-temperature structural and dielectric properties of cubic perovskite materials such as BaTiO3, SrTiO3, KNbO3, and PbTiO3. These materials display an intriguing variety of ferroelectric, and antiferroelectric, and antiferrodistortive structural phase transitions, and are of particular interest for technological applications in view of their unique dielectric and piezoelectric properties and their widespread use in Navy acoustic transducer (sonar) systems. During the contract period, we succeeded in developing a detailed microscopic understanding of the structural and dielectric properties of many of these materials. In particular, we calculated the structural properties and identified the instabilities for eight materials; we developed a new approach to calculating electric polarization, and used it to compute spontaneous polarizations and dynamical effective charges; we calculated the phase transition sequence for BaTiO3 and SrTiO3 as a function of temperature; we studied the ground-state structure and phonons carefully for PbTiO3; and we carried out studies of domain walls and surfaces in BaTiO3.