Fractional quantum Hall effect with spin reversal

We study the spin polarization of the ground states and the excited states of the fractional quantum Hall effect, using spherical geometry for finite-size systems. In the absence of the Zeeman energy, the ground states at filling 2/q, with q odd, are found to be spin unpolarized and nondegenerate for all values of q studied. The energy differences between the spin-polarized and spin-unpolarized states at {ν}=2/3 and 2/5 are estimated by extrapolating to the thermodynamic limit. The spin polarization of the lowest-energy excitations are studied and the results agree with recent experiments.