When listening to the description of post-HF methods, I was surprised to see the “exact solution” was outside the set of all Slater determinants. My limited understanding is that Hartree-Fock gives the best solution for a *single* Slater determinant, and post-HF methods improve upon that solution by adding more and more excited Slater determinants. If the basis set is large enough, would the “full configuration interaction” solution converge to the exact solution, or is there still a limit to full CI?