For a given molecure, the computation of the nuclear repulsion energy can be done by the sum of the pair-wise Coulomb interaction over the protons. In psi4, the electric field strength can be provided to the mol.nuclear_repulsion_energy function.
How is the electric field taken into account in the computation of the nuclear repulsion energy?
Please stop tagging your questions as “Psi4Education,” as they have nothing to do with Psi4Education. Psi4Education is about using Psi4 for computational chemistry labs in undergraduate and graduate education. You’re clearly asking about a research project.
mol.nuclear_repulsion_energy is more precisely the “electron-independent” energy contributions, so it accounts for the interaction of the nuclei with the external electric field, if any. In the typical case, the external electric field is zero, and the function reduces to the nuclear_repulsion_energy.