  We present an efficient implementation of the Generalized Green's function
Cluster Expansion (GGCE), which is a new method for computing the ground-state
properties and dynamics of polarons (single electrons coupled to lattice
vibrations) in model electron-phonon systems. The GGCE works at arbitrary
temperature and is well suited for a variety of electron-phonon couplings,
including, but not limited to, site and bond Holstein and Peierls
(Su-Schrieffer-Heeger) couplings, and couplings to multiple phonon modes with
different energy scales and coupling strengths. Quick calculations can be
performed efficiently on a laptop using solvers from NumPy and SciPy, or in
parallel at scale using the PETSc sparse linear solver engine.
