  Qualitatively different systems of molecular energy bands are studied on
example of a parametric family of effective Hamiltonians describing rotational
structure of triply degenerate vibrational state of a cubic symmetry molecule.
The modification of band structure under variation of control parameters is
associated with a topological invariant "delta-Chern". This invariant is
evaluated by using a local Hamiltonian for the control parameter values
assigned at the boundary between adjacent parameter domains which correspond to
qualitatively different band structures.
