Treatment of internal conversion in complex systems is nothing new, if not much more difficult from first principles. For many systems, simple approximations can be made to incorporate complex electronic interactions. The most common and prolific is that of the polarisable continuum model, whereby a solvent is simulated using a series of point charges acting as a dielectric cavity. However, there are also many systems which are highly sensitive to their environment, where this approximation breaks down. In this case alternative methods are required, and due to their computational complexity may be semi-empirical or entirely within classical mechanics. While this review is opting to focus on first principle treatments of internal conversion, here we will briefly discuss semi-classical methods to examine excitonic recombination. See Ref. for a comprehensive review.