Strong correlation in incremental full configuration interaction.

Area of Science:

• Quantum Chemistry
• Computational Chemistry
• Materials Science

Background:

• Accurate calculation of electronic energies is crucial for understanding chemical reactions and material properties.
• Traditional methods like Full Configuration Interaction (FCI) are computationally expensive for larger systems.
• Incremental methods like iFCI offer a more scalable approach to high-accuracy energy calculations.

Purpose of the Study:

• To introduce and validate the Perfect Pairing iFCI (PP-iFCI) method.
• To assess the performance of PP-iFCI in describing strong correlation in molecular systems.
• To demonstrate the applicability of PP-iFCI for accurate ground-state computations of polyatomic molecules.

Main Methods:

• The study replaces the Hartree-Fock reference in the original iFCI method with the Perfect Pairing (PP) ansatz.
• The PP-iFCI method utilizes a many-body expansion of the correlation energy.
• The method was tested on single, double, and triple bond dissociations of main group polyatomics using double and triple zeta basis sets.

Main Results:

• PP-iFCI captures a significant portion of correlation energy at the zero-order level.
• The method demonstrates size consistency and size extensivity.
• PP-iFCI yields smooth dissociation profiles, indicating its ability to handle strong correlation.
• Accurate FCI-quality ground state computations are achievable for systems up to approximately 10 heavy atoms.

Conclusions:

• PP-iFCI offers a computationally efficient and accurate method for electronic structure calculations.
• The PP-iFCI approach significantly improves upon the original iFCI method by incorporating the PP ansatz.
• This advancement makes high-accuracy quantum chemical calculations feasible for a broader range of chemically relevant systems.