  The properties of large bipolarons in two and three dimensions are
investigated by averaging over the relative wavefunction of the two electrons
and using the Lee-Low-Pines-Huybrechts variational method. We obtain the
ground-state (GS) and excited-state energies of the Fr\"{o}hlich bipolaron for
the whole range of electron-phonon coupling constants. Furthermore, we
calculate the energies of the first relaxed excited state (RES) and
Franck-Condon (FC) excited state of the bipolaron. Compared with the FC state,
the first RES has a lower energy. Our results for the GS and RES energies are
lower than those obtained before by the Landau-Pekar method in the whole
coupling regime.
