  Quantum dynamics of the electron wave function on one-dimensional lattice is
considered. The lattice consists of $N$ equal sites and one impurity site. The
impurity site differs from other sites by the on-site electron energy $E$ and
the hopping integral $C$. The wave function is located on the impurity site at
$t = 0$. The wave packet is formed which travels along the lattice, and
reflects from its end. Reflections happen many times (Loschmidt echo) and this
phenomenon is considered in the second part of the paper. Analytical
expressions for the wave packet front propagation at different values $E$ and
$C$ are derived, and they are in excellent agreement with the numerical
simulation. The obtained results can help in interpretation of recent
experiments on highly efficient charge transport in synthetic olygonucleotides.
