Knowles Partitioning from a Stationary Condition: Single- and Multireference Case

Area of Science:

• Quantum Chemistry
• Computational Physics
• Theoretical Chemistry

Background:

• Many-body perturbation theory (PT) is crucial for electronic structure calculations.
• Existing methods like Møller-Plesset (MP) partitioning have limitations, especially for multireference (MR) systems.
• Knowles' recent work introduced a novel partitioning scheme.

Purpose of the Study:

• To generalize Knowles partitioning for multireference PT (MRPT) schemes.
• To improve the performance and accuracy of MRPT calculations.
• To address shortcomings in previous MR adaptations of PT.

Main Methods:

• Utilizing a stationary condition on the first-order wave function in PT.
• Optimizing one-body integrals within the first-order interacting subspace.
• Applying the method within the frame multiconfiguration PT (fMCPT) framework, a pivot-independent variant.

Main Results:

• The stationary condition naturally leads to Knowles partitioning.
• The fMCPT method with Knowles partitioning shows superior performance compared to MP partitioning.
• The resulting PT series closely approximates stationary condition-based extensions in complete active space PT (CASPT).

Conclusions:

• Knowles partitioning offers a significant advancement for MRPT calculations.
• This method provides a more accurate and robust alternative to traditional MP partitioning.
• The developed approach rectifies limitations of prior MR adaptations, enhancing computational chemistry tools.