  The transport properties of junctions composed of a central region tunnel
coupled to external electrodes is frequently studied within the single-impurity
Anderson model with Hubbard on-site interaction. In the present work, we
supplement the model with an important ingredient, namely the charge-bond
interaction, also known as correlated or assisted hopping. Correlated hopping
enters the second-quantised Hamiltonian, written in the Wannier representation,
as an off-diagonal many-body term. Using the equation of motion technique, we
study the effect of the correlated hopping on the spectral and transport
characteristics of a two-terminal quantum dot. Two different Green functions
(GFs) appear: one of them describes the spectral properties of the quantum dot,
the other the transport properties of the system. The calculation of the
transport GF requires the knowledge of the spectral one. We use decoupling
procedures similar to those which properly describe the standard Anderson model
within the Kondo regime and outside of it. For an arbitrary ratio $x$ between
the amplitudes of correlated and single-particle hopping terms, the transport
GF fulfils the $x \leftrightarrow 2-x$ symmetry of the model. The average
occupation of the dot also obeys this symmetry, albeit the spectral function of
the quantum dot, calculated within an analogous decoupling scheme as for the
transport GF, does not. We identify the physical reason for this behaviour, and
propose a way to cure it. Since the correlated-hopping term breaks the
particle-hole symmetry of the model and modifies all transport characteristics
of the system, the detailed knowledge of its influence on measurable
characteristics is a prerequisite for its experimental detection. Simple,
experimentally feasible methods are proposed.
