lattice_vector           4.21041000        0.00000000        0.00000000
lattice_vector           0.00000000        4.21041000        0.00000000
lattice_vector           0.00000000        0.00000000        4.21041000
atom          0.000000        0.000000        0.000000  Mg  
atom          0.500000        0.000000        0.000000  O