In Sections 2.2-2.3.2, methods have been introduced that model the interactions with the surrounding medium in an approximate manner. This allows for a very precise description of the electronic structure of the investigated systems, however, as pressure is a macroscopic quantity, it may be necessary to model the medium more explicitly. In a few model studies, noble gases have been used to function as soft confinement potentials compressing linear systems. Miao el al. generalized this approach in the "helium compression chamber" method. Here, an atom is placed in the center of a large periodic box filled with helium atoms modeling the surrounding medium, which is then compressed by reducing the box volume, as shown in Fig. . The helium compression chamber has been used to study electrides and, recently, electronegativities. It must not be forgotten that the approach of using helium atoms as the pressure-transmitting medium is an approximation. In the high pressure regime, this approximation, which models isotropic solvent interaction, does not hold if the "real" solvent has low symmetry. For example, a functional group of the solvent might be pushed into the solute, leading to a stronger local deformation. Hence, it may be Figure : Depiction of helium atoms compressing an inner atom, as used in the helium compression chamber method. Reprinted with permission of Miao et al., Copyright 2014 American Chemical Society.