  The functional integral method can be used in quantum mechanics to find the
scattering amplitude for particles in the external field. We will obtain the
potential scattering amplitude form the complete Green function in the
corresponding external field through solving the Schrodinger equation, after
being separated from the poles on the mass shell, which takes the form of an
eikonal (Glauber) representation in the high energy region and the small
scattering angles. Consider specific external potentials such as the Yukawa or
Gaussian potential, we will find the corresponding differential scattering
cross-sections.
