First principle calculations of domain boundaries in multiferroic BiFeO3

Domain boundaries in ferroic materials deviate from the bulk in both the structural and electronic properties. Their presence in the material influences the total energy of the system, the band structure and the magnetic and electric polarization. We report on a Density Functional Theory (DFT) approach within the Local Density Approximation on domain boundaries in multiferroic BiFeO3 (space group: R3c). Our model systems consist of the experimentally observed 71 degree, 109 degree and 180 degree domain walls. The calculations were performed within the DFT software VASP, incorporating standard pseudopotentials and a plane wave basis set. A complete electronic and ionic relaxation of the model structures has been performed to yield details of the charge and structure modulation at the boundary including the deformation of the Fe-centered oxygen octahedron, the formation of electric dipole layers leading to a jump in the electrostatic potential, band gap narrowing and a domain wall dependent modification of the small ferromagnetic effect present in BiFeO3.