def kspacing(calc, val):
    """This is an ASE keyword for producing a uniform Monkhosrt-Packed grid
    in reciprocal space. The float provided is the minimum distance between
    points in reciprocal space.

    https://wiki.fysik.dtu.dk/ase/ase/calculators/espresso.html
    """
    assert isinstance(val, float)
    assert val >= 0 and val <= 1
