Question on post-HF methods

[jmontgomery@flsouthern.edu]

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?

[Stefaan Cottenier]

Interesting question. It will be dealt with in the feedback webinar.

[carlosjimenez11]

Theoretically, the full CI arises with the exact ground state indeed, however, if you take a look on the central equation for CI, you will note that it’s impossible to consider computationally all the possible configurations even for small systems. So, the answer is yes, the full CI solution converges with the ground state, but its not applicable.

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