  The basic Landau model for uniaxial systems of the II class is nonintegrable,
and allows for various stable and metastable periodic configurations, beside
that representing the uniform (or dimerized) ordering. In the present paper we
complete the analysis of this model by performing the second order variational
procedure, and formulating the combined Floquet-Bloch approach to the ensuing
nonstandard linear eigenvalue problem. This approach enables an analytic
derivation of some general conclusions on the stability of particular states,
and on the nature of accompanied collective excitations. Furthermore, we
calculate numerically the spectra of collective modes for all states
participating in the phase diagram, and analyze critical properties of
Goldstone modes at all second order and first order transitions between
disordered, uniform and periodic states. In particular it is shown that the
Goldstone mode softens as the underlying soliton lattice becomes more and more
dilute.
