As can be seen, McWeeny's GFT formulas are fully analogous to the Slater-Condon expressions for the matrix elements of the electronic Hamiltonian in the basis of Slater determinants (SDs), with fragments playing the role of electrons and site states playing the role of molecular orbitals (MOs). If the bra and ket products are equal, the matrix element includes the sum of site energies (instead of the sum of orbital energies), interfragment nuclear-electron interaction integrals (instead of 1-electron integrals), and interfragment electron-electron interaction and exchange integrals (instead of 2-electron integrals). If the bra and ket products differ in one site state, the coupling contains nuclearelectron and electron-electron integrals. If they differ in two site states, the coupling includes only electron-electron integrals. The Kronecker deltas in the J term (Equation ( )) serve as switches to include the respective terms depending on the number of differing site states. Note, however, that the aforementioned analogy be-tween GFT and regular electronic structure theory does not hold perfectly-the fragments are distinguishable whereas electrons are indistinguishable, and the site states are not one-but rather multi-fermionic functions themselves.