  The framework of relativistic energy density functionals is extended to
include correlations related to restoration of broken symmetries and
fluctuations of collective variables. A new implementation is developed for the
solution of the eigenvalue problem of a five-dimensional collective Hamiltonian
for quadrupole vibrational and rotational degrees of freedom, with parameters
determined by constrained self-consistent relativistic mean-field calculations
for triaxial shapes. The model is tested in a series of illustrative
calculations of potential energy surfaces and the resulting collective
excitation spectra and transition probabilities of the chain of even-even
gadolinium isotopes.
