  We study the domain formation in the v=2/3 fractional quantum Hall systems
basing on the density matrix renormalization group (DMRG) analysis. The
ground-state energy and the pair correlation functions are calculated for
various spin polarizations. The results confirm the domain formation in
partially spin polarized states, but the presence of the domain wall increases
the energy of partially spin polarized states and the ground state is either
spin unpolarized state or fully spin polarized state depending on the Zeeman
energy. We expect coupling with external degrees of freedom such as nuclear
spins is important to reduce the energy of partially spin polarized state.
