  We have developed an efficient method for quantum number projection from most
general HFB type mean-field states, where all the symmetries like axial
symmetry, number conservation, parity and time-reversal invariance are broken.
Applying the method, we have microscopically calculated, for the first time,
the energy spectra based on the exotic tetrahedral deformation in
$^{108,110}$Zr. The nice low-lying rotational spectra, which have all
characteristic features of the molecular tetrahedral rotor, are obtained for
large tetrahedral deformation, $\alpha_{32} \gtsim 0.25$, while the spectra are
of transitional nature between vibrational and rotational with rather high
excitation energies for $\alpha_{32}\approx 0.1-0.2$

Nuclear Theory