  As possible states to characterize THz wave emission from intrinsic Josephson
junctions without external fields, the McCumber-like state and $\pi$-phase-kink
state have been proposed. In the present article it is numerically shown that
both states are stationary according to the bias current $J$ and surface
impedance $Z$. The McCumber-like state is stable for low $J$ and small $Z$. For
higher $J$, the $\pi$-phase-kink state accompanied with symmetry breaking along
the c axis is stable even for Z=1, though strong emission in the vicinity of
cavity resonance points only takes place for larger $Z$. Different emission
behaviors for Z=1 and 10 are precisely compared. The dynamical phase diagram
for $1 \le Z \le 10$ and the optimal value of $Z$ for the strongest emission
are also evaluated.
