def METHOD_NAME():
    """
    This function constructs the input file for the GS calculation:
    """
    # Initialize MgO structure from abinit variables.
    structure = abilab.Structure.from_abivars(
        acell=3 * [4.252718 * abilab.units.ang_to_bohr],
        rprim=[0.0000000000, 0.5000000000, 0.5000000000,
               0.5000000000, 0.0000000000, 0.5000000000,
               0.5000000000, 0.5000000000, 0.0000000000],
        natom=2,
        ntypat=2,
        typat=[1, 2],
        znucl=[12, 8],
        xred=[0.0000000000, 0.0000000000, 0.0000000000,
              0.5000000000, 0.5000000000, 0.5000000000]
    )
    # NC pseudos assumed in currect working directory.
    pseudos = ["Mg-sp-gw.psp8", "O.psp8"]
    # Input for GS part.
    gs_inp = abilab.AbinitInput(structure, pseudos=pseudos)
    gs_inp.set_vars(
        nband=16,
        paral_kgb=0,
        ecut=35.0,        # Too low. Should be ~50
        ngkpt=[4, 4, 4],  # Too coarse
        #nshiftk=1,
        shiftk=[0, 0, 0], # Gamma-centered mesh. Important to have the CBM/VBM!
        tolvrs=1.0e-10,
        diemac=9.0,
        nstep=150,
        nbdbuf=4,
        #prtpot=1,       # Print potential for Sternheimer
        iomode=3,        # Produce output files in netcdf format.
    )
    return gs_inp