  In this work we demonstrate that accurate ground state wave functions may be
constructed for polarons in a fully ab initio setting across the wide range of
couplings associated with both the large and small polaron limits. We present a
single general unitary transformation approach which encompasses an ab initio
version of the Lee-Low-Pines theory at weak coupling and the coherent state
Landau-Pekar framework at strong coupling while interpolating between these
limits in general cases. We show that perturbation theory around these limits
may be performed in a facile manner to assess the accuracy of the approach, as
well as provide an independent route to the ab initio properties of polarons.
We test these ideas on the case of LiF, where the electron-polaron is expected
to be large and relatively weakly coupled, while the hole-polaron is expected
to be a strongly coupled small polaron.
