@classmethod
def get_kinetic_energy_cutoff_wavefunctions(cls, calc, **kwargs):
    """Return kinetic energy cutoff for wavefunctions in eV."""
    from qe_tools.constants import ry_to_ev
    parameters = calc.inputs.parameters
    ecutwfc = None
    try:
        ecutwfc = parameters.get_dict()['SYSTEM']['ecutwfc']
    except KeyError:
        pass
    if ecutwfc is None:
        return None
    return ecutwfc * ry_to_ev
