  We have proposed several 1D and 2D electronic models with the exact ground
state. The ground state wave function of these models is represented in terms
of "singlet bond" functions consisting of homopolar and ionic configurations.
The Hamiltonians of the models include the correlated hopping of electrons,
pair hopping terms and the spin interactions. One of the 1D models demonstrates
spontaneous breaking of the translational symmetry. We studied also the model
describing the transition point between the phases with and without an
off-diagonal long-range order.
