Figure 4. Graphical representation of FMO-based fragmentation results.
For the FMO method, charge partitioning makes auto fragmentation difficult. Because exchange and self-consistency are local in most molecules, non-local regions are treated using the coulomb operator, and molecular calculations are performed individually within the overall system’s coulomb field. The coulomb bath allows for fragmentation without hydrogen capping. For proteins, fragments can be generated automatically by breaking the Cα–C(O) bond. After fragmentation (Figure 4), a specific number of electrons are assigned to each fragment according to bond-attached atom, bond-detached atom, and DUMMY, which mimics the coulomb field. The fragments’ molecular orbitals and the contributions from pairs of fragments are calculated to account for the molecule’s total energy.