  We are concerned with the stability of formation of large bipolaron in a
3-dimensional (3D) crystal. This problem is considered in the framework of
nonrelativistic quantum field theory. Thus, the Hamiltonian formalism, as
Froehlich introduced, is employed to describe the bipolaron. We approach the
problem by characterizing some sufficient or necessary conditions for the
bipolaron being stable. This paper gives a full detail of the author's talks at
ESI, RIMS, and St. Petersburg State Univ. in 2005.

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