Structural and electronic properties of cubic KNbO <inf>3</inf> (0 0 1) surfaces: A first-principles study

We present the calculations of the cubic perovskite KNbO 3 (0 0 1) surface with NbO 2 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 NbO 2 -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 NbO 2 termination, revealing that it takes much less energy to cleave on NbO 2 plane than on a KO plane. The band gaps for KO-terminated and NbO 2 -terminated surface are 1.70 and 1.30 eV, respectively. Mulliken population analysis shows the strong increase in the K-O chemical bonding on the top surface of the KO-terminated slab and significant covalency for Nb-O bonding