Polynomial scaling approximations and dynamic correlation corrections to doubly occupied configuration interaction...

Area of Science:

• Quantum Chemistry
• Computational Chemistry
• Theoretical Chemistry

Background:

• Configuration Interaction (CI) methods are crucial for describing electron correlation in molecules.
• Doubly Occupied Configuration Interaction (DOCI) offers a simplified yet powerful approach to capture static correlation.
• Accurate description of both static and dynamic correlation remains a challenge in quantum chemistry.

Purpose of the Study:

• Introduce novel polynomial scaling methods to approximate DOCI wave functions.
• Enhance the description of dynamic correlation beyond traditional DOCI.
• Develop and evaluate efficient orbital optimization algorithms for DOCI methods.

Main Methods:

• Developed polynomial scaling approximations for DOCI wave functions.
• Introduced and compared energy-based (simulated annealing) and seniority number minimizing orbital optimization algorithms.
• Assessed wave function accuracy by comparing energies and overlaps with Full Configuration Interaction (FCI).

Main Results:

• The new methods successfully approximate DOCI wave functions and improve dynamic correlation.
• Low energy does not always correlate with a good approximation of the exact wave function.
• The seniority number minimizing algorithm provides a computationally affordable and effective alternative for orbital optimization.

Conclusions:

• The novel DOCI-based wave functions are well-suited for computationally efficient descriptions of static correlation.
• These methods offer a promising approach for capturing dynamic correlation to a lesser extent.
• Careful selection of the orbital basis is crucial for the performance of these DOCI approximations.