  We apply the approximate analytic methods to the investigation of the band
structure of the asymmetric Hubbard model where the chemical potentials and
electron transfer parameters depend on the electron spin (type of
quasiparticles). The Hubbard-I and alloy-analogy approximations are the
simplest approximations which are used. Within the alloy-analogy approximation,
the energy band of particles does not depend on the transfer parameter of
particles of another sort. It means that the gap in the spectrum opens at the
critical value $U_{c}$ that is the same in two different limiting cases: the
Falicov-Kimball model and the standard Hubbard model. The approximate analytic
scheme of the dynamical mean-field theory is developed to include into the
theory the scattering of particles responsible for the additional mechanism
(due to the transfer of particles of another sort) of the band formation. We
use the so-called GH3 approach that is a generalization of the Hubbard-III
approximation. The approach describes the continuous Mott transition with the
$U_{c}$ value dependent on a ratio of transfer parameters of different
particles.
