def check_spin_polarization(Par):
    """
    The function checks if a spin-polarized system should be calculated
    and sets some default parameters.
    """
    if hasattr(Par, 'Population'):
        popu = Par.Population
        ispopu = True
        rho_0 = Par.rho_0
    else:
        popu = None
        ispopu = False
        rho_0 = None
    return popu, ispopu, rho_0
