  It was shown that an infinite convergent sequence of improving non-increasing
upper bounds to the ground state energy of a slow-moving acoustical polaron can
be obtained by means of generalized variational method. The proposed approach
is especially well-suited for massive analytical and numerical computations of
experimentally measurable properties of realistic polarons and can be
elaborated even further, without major alterations, to allow for treatment of
various polaron-type models.
