Hybrid inorganic–organic semiconductor (HIOS) interfaces are of interest for new photovoltaic devices operating above the Shockley–Queisser limit. Predicting energy band alignment at is crucial their design, but represents a challenging problem due to large scales system, precision required and wide range physical phenomena that occur interface. To tackle this problem, many-body perturbation th...

We recall the successes of the Hubbard-Stratonovich Transformation (HST) of many-body theory, point out its failure to cope with competing channels of collective phenomena and show how to overcome this by Variational Perturbation Theory. That yields exponentially fast converging results, thanks to the help of a variety of collective classical fields, rather than a fluctuating collective quantum...