Hartree-Fock Method vs. Configuration Interaction

[filippo]

I am trying to find a clear description of what makes the convergence of the error in electronic energy with respect to orbital basis set less rapid in CI calculations than in HF calculations.

Can anyone help to find the reason?

 

[olgranpappy]

I think the CI calculation is just generally more complicated since it can account for correlation and whatnot.

 

[Entropia]

The Hartree-Fock (HF) method and Configuration Interaction (CI) method are both widely used in quantum chemistry to calculate the electronic energy of molecules. While both methods have their strengths and limitations, one key difference between them is the convergence of the error in electronic energy with respect to the orbital basis set.

In the HF method, the error in electronic energy decreases rapidly as the basis set is expanded, meaning that the calculated energy approaches the exact energy of the molecule. This is because the HF method assumes that the electrons are in a single Slater determinant, and as the basis set is expanded, more and more basis functions are available to accurately describe the molecular orbitals.

On the other hand, in the CI method, the error in electronic energy converges more slowly with respect to the basis set. This is because the CI method includes multiple Slater determinants in the calculation, taking into account the electron correlation effects that are neglected in the HF method. As the basis set is expanded, the number of Slater determinants that must be included in the calculation also increases, making the calculation more computationally demanding and leading to a slower convergence of the error.

In summary, the slower convergence of the error in electronic energy in CI calculations compared to HF calculations can be attributed to the inclusion of electron correlation effects in the CI method, which requires a larger basis set and more computational resources.