  Single-reference coupled-cluster theory is an accurate and affordable
computational method for the nuclear many-body problem. For open-shell nuclei,
the reference state typically breaks rotational invariance and angular momentum
must be restored as a good quantum number. We perform angular-momentum
projection after variation and employ the disentangled coupled-cluster
formalism and a Hermitian approach. We compare our results with benchmarks for
$^8$Be and $^{20}$Ne using a two-nucleon interaction from chiral effective
field theory and for $pf$-shell nuclei within the traditional shell model. We
compute the rotational band in the exotic nucleus $^{34}$Mg and find agreement
with data.
