An Improved Size-Consistent Second-Order Brillouin-Wigner Perturbation Theory: Which Desirable Properties Are...

Area of Science:

• Quantum Chemistry
• Computational Chemistry
• Theoretical Chemistry

Background:

• Second-order Brillouin-Wigner perturbation (BW-s2) theory aims for size-consistency.
• Conventional BW-s2 theory can be conditionally size-consistent, requiring specific orbital choices.
• Hamiltonian repartitioning is key to achieving size-consistency in perturbation theories.

Purpose of the Study:

• To explore desirable parameter choices (α, γ) for a size-consistent BW-s2 theory.
• To identify parameters that ensure numerical stability, accuracy, and unconditional size-consistency.
• To evaluate the performance of BW-s2(α, γ) for chemical energy differences and dissociation processes.

Main Methods:

• Investigated Hamiltonian repartitioning strategies for BW-s2 theory.
• Analyzed parameter choices (α, γ) based on criteria including size-consistency, accuracy, and dissociation behavior.
• Tested BW-s2(α, γ) on bond-dissociation curves and 14 datasets of chemical energy differences.

Main Results:

• Established stronger constraints for unconditional size-consistency in BW-s2 (α + γ > 1).
• Recommended BW-s2(α=2, γ=2) as a nonempirical choice ensuring unconditional size-consistency, accuracy, and desirable dissociation properties.
• Identified BW-s2(α=4, γ=0) as an alternative nonempirical choice sacrificing exactness and particle-hole symmetry at dissociation.

Conclusions:

• The BW-s2(α=2, γ=2) parameterization provides a robust and accurate method for quantum chemical calculations.
• This choice offers unconditional size-consistency, crucial for reliable predictions of molecular properties.
• The study provides valuable insights into optimizing perturbation theories for computational chemistry applications.