The approach of Artyukhov & Galeeva based on the work of Plotnikov, while important to the state of the art, is severely limited. Applicable only to biological systems with light atoms (H, C, N , O, F , S, Cl), the Plotnikov-Robinson-Jortner model cannot be used for organometallic systems for example. Further, use of the model has found issues with treatment of complex chromophores like porphyrins and circulenes , since the partial neglect of differential overlapping method is lacking in its ability to model excitation energies. In looking for ways to scaffold this issue, Valiev and co-workers first examined the photophysics of a series of complex chromophores, and highlighted the difference between rates calculated using density functional theory and extended multi-configuration quasi-degenerate second-order perturbation theory , compared to second-order coupledcluster calculations when the vertical excitation energies were calculated using first principles or semi-empirical methods. Similar work was performed by Baryshnikov and co-workers in the same vein. Following this work, propulsion towards hybridisation with modern quantum chemical techniques was undertaken to incorperate first principle non-adiabatic coupling matrix elements, then incorporating more technical effects like Herzberg-Teller contributions , and anharmonic effects , entirely removing the need for semi-empiricism.