Structural and electronic properties of cubic KNbO3 (0Â 0Â 1) surfaces: A first-principles study

We present the calculations of the cubic perovskite KNbO3 (0 0 1) surface with NbO2 and KO terminations within the first-principles density functional theory. The electronic structure, surface energy, and charge distribution for both termination are calculated. For the case of NbO2-terminated surfaces, the largest atomic relaxation is in the first-layer atoms, while for KO terminations in the second-layer atoms. The surface energy for the KO terminated was 1.21 eV, higher than the calculated surface energy of 0.75 eV for NbO2 termination, revealing that it takes much less energy to cleave on NbO2 plane than on a KO plane. The band gaps for KO-terminated and NbO2-terminated surface are 1.70 and 1.30 eV, respectively. Mulliken population analysis shows the strong increase in the KO chemical bonding on the top surface of the KO-terminated slab and significant covalency for NbO bonding.