  We derive the effective low energy Hamiltonian for the tight-binding model
with the hopping integral slowly varying along the chain. The effective
Hamiltonian contains the kinetic energy with position dependent mass, which is
inverse to the hopping integral, and effective potential energy. Changing of
ordering in the kinetic energy leads to change of the effective potential
energy and leaves the Hamiltonian the same one. Therefore, we can choose
arbitrary von Roos ordering parameters in the kinetic energy without changing
the Hamiltonian. Moreover, we propose a more general form for the kinetic
energy than that of von Roos, which nevertheless together with the effective
potential energy represent the same Hamiltonian.
