Generalized Møller-Plesset Partitioning in Multiconfiguration Perturbation Theory

Area of Science:

• Quantum Chemistry
• Theoretical Chemistry

Background:

• Perturbation theory (PT) is crucial for refining approximate solutions in quantum mechanics.
• Multiconfiguration (MC) methods are essential for describing systems with strong electron correlation.
• Existing multireference perturbation theories (MRPT) have limitations in computational efficiency and applicability.

Purpose of the Study:

• To develop novel perturbation theories based on multiconfiguration zero-order functions.
• To provide a generalized Møller-Plesset (MP) second-order correction applicable to various reference functions.
• To establish a computationally feasible approach for electronic structure calculations.

Main Methods:

• Development of two new perturbation theories utilizing biorthogonal vector sets.
• Implementation using the full Fockian, leading to a nondiagonal zero-order resolvent matrix.
• Assessment of performance using antisymmetric product of strongly orthogonal geminal (APSG) wave functions as reference.

Main Results:

• The developed theories offer a simple, generalized second-order Møller-Plesset (MP) correction.
• Computational cost is comparable to single-reference MP theory due to iterative Fockian inversion.
• The theories are applicable to both complete and incomplete model spaces.

Conclusions:

• The new perturbation theories provide a versatile tool for improving reference functions in quantum chemistry.
• The approach offers a balance between accuracy and computational efficiency for electronic structure problems.
• Further investigation into the relationship with existing multireference perturbation theory formalisms is warranted.