In a DFT standard calculation of a solid 3D material (i.e. bulk metal), one of the properties that can be obtained is the Fermi level $E_F$. This feature is related with the required work to add an electron to this material.
In organic electronics, one possible utility of that value is to extract information about the charge-transfer properties of such material when it is contacted by a single molecule or even a molecular layer (organic semiconductor), thus obtaining the interfacial properties of the complete junction. As the orbitals of both entities tend to hybridize, the properties of the modified surface can be radically different from those of the initial isolated materials. This is particularly critical when either or both of the materials are magnetic, in which case it is called Spinterface.
In this context, some question arises. Which is the most adequate way of calculating a molecular surface on top of a metal? How to account on rearrangement of atomic positions, image-charge properties and orbital hybridization? and last but not least, How to model a descriptive molecular surface in which different molecules can be arranged in different positions?