The formation of dipoles at interfaces between organic semiconductors is expected to play a significant role in the operation of organic-based devices, though the electronic processes at their origin have still to be clearly elucidated. Quantum-chemical calculations can prove very useful to shed light on such electronic interfacial phenomena provided that a suitable theoretical approach is used. In this context, we have performed calculations on small vertical stacks of TTF-TCNQ molecules, first at the CAS-MRCI level to validate the use of single-determinantal approaches, then at the MP2 level set as a benchmark. Various density functional theory (DFT) functionals have then been applied to larger stacks, showing that long-range corrected functionals are required to reproduce MP2 results taken as benchmark. Finally, the use of periodic boundary conditions at the DFT level points to the huge impact of depolarization effects between adjacent stacks.