def METHOD_NAME():
    """Combines the smirnoff99Frosst and tip3p offxml files
    into a single one which can be consumed by the property
    estimator.
    Returns
    -------
    SmirnoffForceFieldSource
        The force field containing both smirnoff99Frosst-1.1.0
        and TIP3P parameters
    """
    from openff.toolkit.typing.engines.smirnoff import ForceField
    smirnoff_force_field_path = "smirnoff99Frosst-1.1.0.offxml"
    tip3p_force_field_path = get_data_filename("forcefield/tip3p.offxml")
    smirnoff_force_field_with_tip3p = ForceField(
        smirnoff_force_field_path, tip3p_force_field_path
    )
    return SmirnoffForceFieldSource.from_object(smirnoff_force_field_with_tip3p)