# Can you model intermolecular interactions by using the Born-Oppenheimer approximation to get a potential function for nuclei?

Here is a claim about the modeling of chemical systems. I can’t remember if it’s true or not:

Suppose we have a bunch of molecules and we want to know how they interact. Eg we want to look at the physics of two $\ce{CO_2}$ molecules bumping into each other. We can do this by treating the nuclei as classical particles moving in a potential function determined by the ground state electronic wavefunction for a given configuration of nuclei.

Eg, we want to know how hydrogen molecules bounce off each other. We do this by modeling it as two protons with momentums and positions, and we iterate forward through time using a Hamiltonian where the potential energy operator uses the Hartree-Fock method or something to calculate the electronic potential.

This approximation obviously ignores some important things, for example the momentum of electrons. But that’s small compared to the momentum of the nuclei and plausibly doesn’t matter.

Is this approximation good? Is it commonly used?