  The structures of excited states in $^{34}$S are investigated using the
antisymmetrized molecular dynamics and generator coordinate method (GCM). The
GCM basis wave functions are calculated via energy variation with a constraint
on the quadrupole deformation parameter $\beta$. By applying the GCM after
parity and angular momentum projections, the coexistence of two positive- and
one negative-parity superdeformed (SD) bands are predicted, and low-lying
states and other deformed bands are obtained. The SD bands have structures of
$^{16}$O + $^{16}$O + two valence neutrons in molecular orbitals around the two
$^{16}$O cores in a cluster picture. The configurations of the two valence
neutrons are $\delta^2$ and $\pi^2$ for the positive-parity SD bands and
$\pi^1\delta^1$ for the negative-parity SD band. The structural changes of the
yrast states are also discussed.
