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.