  In this paper we obtain asymptotic formulas of arbitrary order for the Bloch
eigenvalue and the Bloch function of the periodic Schrodinger operator of
arbitrary dimension, when corresponding quasimomentum lies near a diffraction
hyperplane. Moreover, we estimate the measure of the isoenergetic surfaces in
the high energy region. Bisides, writing the asymptotic formulas for the Bloch
eigenvalue and the Bloch function, when corresponding quasimomentum lies far
from the diffraction hyperplanes, obtained in my previous papers in improved
and enlarged form, we obtain the complete perturbation theory for the
multidimensional Schrodinger operator with a periodic potential.
