A plane wave cutoff of 520 eV has been chosen for the wave functions, and a convergency within 1 × 10 -5 eV per supercell. The p and s semi-core states are treated as valence states for the transitions metals and Ca, respectively. To properly describe the strongly correlated 3d-electrons, the Hubbard U corrections 59 on the transition metal 3d orbitals are set to U V = 3.25 eV, U Cr = 3.70 eV, U Mn = 3.90 eV, U Fe = 5.30 eV, U Co = 3.32 eV, and U Ni = 6.20 eV. For Ti, only conventional GGA-RPBE functional is used without the U parameter. A 4×4×3 k-point mesh has been used for the unit cell of CaMO 3 containing four formula units, while the slab calculations performed using a gamma centred k-point grid. The initial configurations are taken from the Materials Project (MP) database . We used the Pnma space group for CaMO 3 perovskites, crystallizing in a face-centered cubic structure. All atomic positions are optimized without symmetry constraints to reach the theoretical ground state configurations. To describe correctly van der Waals interactions resulting from dynamical correlations between fluctuating charge distributions, DFT-D3 61 method with Becke-Jonson damping has been applied in all the calculations. For periodic slab calculations, slabs of five layers in (001) direction are separated by atleast 26 Å of vacuum to prevent interactions due to periodic boundary conditions. Along the (001) direction, CaMO 3 consists of alternating CaO and MO 2 layers. We consider the optimized supercell of ideal MO 2 terminated surface. To keep the symmetry and cancel the artificial interaction between the system and its periodic images, on the top and bottom of the slabs, we have equivalent surfaces both covered by 32 water-molecules. All atomic positions of the slabs are allowed to relax. Spin polarized is considered in all the calculations.