Fragment-based methods decompose a large molecular system into smaller fragments that can be solved independently. In the Divide-and-Conquer (DC) method, the system is divided into overlapping fragments, and each fragment is solved separately. The results are then combined to obtain the properties of the entire system. The Fragment Molecular Orbital (FMO) method takes a similar approach but focuses on the electronic structure, making it particularly useful for studying large biological molecules and complex catalytic systems.
