Multiscale methods allow to model the effect of a specific environment on a system of interest.

Among them, Frozen-Density Embedding Theory (FDET) is an exact theory based on DFT where the system of interest is modelled by means of a wavefunction, and the surrounding environment by means of its electron density, while keeping a quantum-mechanical treatment for the whole space.

There are several options to obtain the environment density. Each of these interplays with specific aspects of FDET and of the approximations made in practical calculations in ways which are not easy to predict.

This work investigates both the relation between the environment density and the quality of the results and novel options to obtain the environment density.