How to use the abipy.data.structure_from_ucell function in abipy

def make_scf_input(ecut=10, ngkpt=(8, 8, 8)):
    """
    This function constructs an `AbinitInput` for performing a
    GS-SCF calculation in crystalline AlAs.

    Args:
        ecut: cutoff energy in Ha.
        ngkpt: 3 integers specifying the k-mesh for the electrons.

    Return:
        `AbinitInput` object
    """
    # Initialize the AlAs structure from an internal database. Use the pseudos shipped with AbiPy.
    gs_inp = abilab.AbinitInput(structure=abidata.structure_from_ucell("AlAs"),
                                pseudos=abidata.pseudos("13al.981214.fhi", "33as.pspnc"))

    # Set the value of the Abinit variables needed for GS runs.
    gs_inp.set_vars(
        nband=4,
        ecut=ecut,
        ngkpt=ngkpt,
        nshiftk=1,
        shiftk=[0.0, 0.0, 0.0],
        ixc=7,
        nstep=500,
        iscf=7,
        diemac=5.0,
        toldfe=1.0e-22,
        nbdbuf=0,
        kptopt=1,

def make_scf_nscf_inputs(nsppol, paral_kgb=1):
    """
    Generate two input files for the GS and the NSCF run for given `nsppol`.
    """
    # Fe normal bcc structure for test of a ferromagnetic calculation
    multi = abilab.MultiDataset(structure=data.structure_from_ucell("Fe-fm"),
                                pseudos=data.pseudos("26fe.pspnc"), ndtset=2)

    # Global variables
    global_vars = dict(
        nsppol=nsppol,
        ecut=18,
        nband=8,
        occopt=3,
        tsmear=0.01,
        paral_kgb=paral_kgb,
    )
    if nsppol == 2:
        global_vars.update(spinat=[0.0, 0.0, 4.0])

    multi.set_vars(global_vars)

def make_base_flow(options):
    multi = abilab.MultiDataset(structure=data.structure_from_ucell("GaAs"),
                                pseudos=data.pseudos("31ga.pspnc", "33as.pspnc"), ndtset=5)

    # Global variables
    kmesh = dict(ngkpt=[4, 4, 4],
                 nshiftk=4,
                 shiftk=[[0.5, 0.5, 0.5],
                         [0.5, 0.0, 0.0],
                         [0.0, 0.5, 0.0],
                         [0.0, 0.0, 0.5]]
    )

    paral_kgb = 1
    global_vars = dict(ecut=2, paral_kgb=paral_kgb)
    global_vars.update(kmesh)

    multi.set_vars(global_vars)

def build_flow(options):
    # Set working directory (default is the name of the script with '.py' removed and "run_" replaced by "flow_")
    if not options.workdir:
        options.workdir = os.path.basename(__file__).replace(".py", "").replace("run_", "flow_")

    structure = abidata.structure_from_ucell("GaAs")
    pseudos = abidata.pseudos("Ga-low_r.psp8", "As_r.psp8")
    num_electrons = structure.num_valence_electrons(pseudos)
    #print("num_electrons:", num_electrons)

    # Usa same shifts in all tasks.
    ngkpt = [4, 4, 4]
    shiftk= [
        [0.5, 0.5, 0.5],
        [0.5, 0.0, 0.0],
        [0.0, 0.5, 0.0],
        [0.0, 0.0, 0.5],
    ]

    # NSCF run on k-path with large number of bands
    kptbounds = [
        [0.5, 0.0, 0.0],  # L point

def build_flow(options, paral_kgb=0):
    """
    Build flow for the calculation of optical properties with optic + band structure
    along high-symmetry k-path. DDK are computed with 3 k-meshes of increasing density
    to monitor the convergece of the spectra.
    """
    # Working directory (default is the name of the script with '.py' removed and "run_" replaced by "flow_")
    workdir = options.workdir
    if not options.workdir:
        workdir = os.path.basename(__file__).replace(".py", "").replace("run_", "flow_")

    multi = abilab.MultiDataset(structure=abidata.structure_from_ucell("GaAs"),
                                pseudos=abidata.pseudos("31ga.pspnc", "33as.pspnc"), ndtset=2)

    # Usa same shifts in all tasks.
    shiftk= [[0.5, 0.5, 0.5],
             [0.5, 0.0, 0.0],
             [0.0, 0.5, 0.0],
             [0.0, 0.0, 0.5]]

    # Global variables.
    multi.set_vars(ecut=2, paral_kgb=paral_kgb)

    # Dataset 1 (GS run)
    multi[0].set_vars(tolvrs=1e-8, nband=4)
    multi[0].set_kmesh(ngkpt=[4, 4, 4], shiftk=shiftk)

    # NSCF run on k-path with large number of bands

def make_scf_input(ngkpt):
    """
    This function constructs the input file for the GS calculation:
    """
    structure = abidata.structure_from_ucell("AlAs")
    pseudos = abidata.pseudos("13al.981214.fhi", "33as.pspnc")
    gs_inp = abilab.AbinitInput(structure, pseudos=pseudos)

    gs_inp.set_vars(
        nband=6,
        ecut=6.0,
        ngkpt=ngkpt,
        nshiftk=1,
        shiftk=[0, 0, 0],
        tolvrs=1.0e-10,
    )

    return gs_inp

def build_flow(options):
    # Working directory (default is the name of the script with '.py' removed and "run_" replaced by "flow_")
    if not options.workdir:
        options.workdir = os.path.basename(sys.argv[0]).replace(".py", "").replace("run_", "flow_")

    pseudos = data.pseudos("14si.pspnc", "6c.pspnc")
    structure = data.structure_from_ucell("SiC")

    # Initialize the input
    relax_inp = abilab.AbinitInput(structure, pseudos=pseudos)

    # Set variables
    relax_inp.set_vars(
        ecut=20,
        paral_kgb=1,
        iomode=3,
        # Relaxation part
        ionmov=2,
        optcell=1,
        strfact=100,
        ecutsm=0.5,       # Important!
        dilatmx=1.15,     # Important!
        toldff=1e-6,

def make_inputs(paral_kgb=1):
    """
    Returns a tuple of 4 input files for SCF, NSCF, SCR, SIGMA calculations.
    These files are then used as templates for the convergence study
    wrt ecuteps and the number of bands in W.
    """
    multi = abilab.MultiDataset(abidata.structure_from_ucell("SiC"),
                                pseudos=abidata.pseudos("14si.pspnc", "6c.pspnc"), ndtset=4)

    ecut = 12
    global_vars = dict(
        ecut=ecut,
        istwfk="*1",
        paral_kgb=paral_kgb,
        gwpara=2,
        iomode=1,
    )

    ecuteps = 4
    ngkpt = [4, 4, 4]
    shiftk = [0, 0, 0]

    multi.set_vars(global_vars)

def make_input(paw=False):
    """
    Build and return an input file for GS calculations with paral_kgb=1
    """
    pseudos = abidata.pseudos("14si.pspnc", "8o.pspnc") if not paw else \
              abidata.pseudos("Si.GGA_PBE-JTH-paw.xml", "o.paw")

    structure = abidata.structure_from_ucell("SiO2-alpha")

    inp = abilab.AbinitInput(structure, pseudos)
    inp.set_kmesh(ngkpt=[1, 1, 1], shiftk=[0, 0, 0])

    # Global variables
    ecut = 24
    inp.set_vars(
        ecut=ecut,
        pawecutdg=ecut * 2 if paw else None,
        paral_kgb=1,
        nsppol=1,
        nband=28,
        npkpt=1,
        npband=1,
        npfft=1,
        fftalg=112,