Static versus dynamically polarizable environments within the many-body $\bf{GW}$ formalism

Continuum or discrete polarizable models for the study of optoelectronic processes in embedded subsystems rely mostly on the restriction of the surrounding electronic dielectric response to its low frequency limit. Such a description hinges on the assumption that the electrons in the surrounding medium react instantaneously to any excitation in the central subsystem, treating thus the environment in the adiabatic limit. Exploiting a recently developed embedded $GW$ formalism, with an environment described at the fully ab initio level, we assess the merits of the adiabatic limit with respect to an environment where the full dynamics of the dielectric response is considered. Further, we show how to properly take the static limit of the environment susceptibility, introducing the so-called Coulomb-hole and screened-exchange contributions to the reaction field. As a first application, we consider a C$_{60}$ molecule at the surface of a C$_{60}$ crystal, namely a case where the dynamics of the embedded and embedding subsystems are similar. The common adiabatic assumption, when properly treated, generates errors below $10\%$ on the polarization energy associated with frontier energy levels and associated energy gaps. Finally, we consider a water molecule inside a metallic nanotube, the worst case for the environment adiabatic limit. The error on the gap polarization energy remains below $10\%$, even though the error on the frontier orbitals polarization energies can reach a few tenths of an electronvolt.