https://mazziotti.uchicago.edu/qcdictionary/e_terms/electron_repulsion_int/index.html Electron repulsion integrals (ERIs) emerge as the two-body (or four-index) expectation values of the Hamiltonian when solving the many-electron Schrödinger equation. These integrals quantify the Coulomb interaction between pairs of electrons over atom-centered basis functions. Hugo en-us