What is the exact Hamiltonian core of the Fragment Molecular Orbital Method?

My major is not chemistry and I am trying to understand the Hamiltonian core of the [Fragment Molecular Orbital (FMO)](https://en.wikipedia.org/wiki/Fragment_molecular_orbital) method.


I think it should be the normal Hamiltonian core of the restricted Hartree-Fock plus two other terms: nuclei attraction between other fragments and the current fragment in the calculation and also the potential energy between them.


But I was wondering If I could get the formula, as I saw in different papers that there are different versions and different formulae associated with that.


