However, the accuracy of classical force fields is inherently limited , and the steep increase in computational effort of more accurate quantum-chemical methods makes them rarely applicable to large biomolecules . For treating excited state phenomena in biological systems and to study excited-state dynamics , quantum-chemical methods are mandatory. Fragmentation methods provide an avenue to decreasing the computational effort of quantum-chemical calculations and to lower its scaling with system size. This is achieved by replacing a calculation for the full system (e.g., a protein) by many small calculations for its fragments (e.g., single amino acids).