A generalized hybrid scheme for multireference methods

Area of Science:

• Quantum Chemistry
• Computational Chemistry
• Theoretical Chemistry

Background:

• Multireference methods are essential for describing electronic structures with strong electron correlation.
• Existing hybrid schemes partition excitation spaces for computational efficiency.
• Recent advancements by Saitow and Yanai introduced a novel hybrid scheme.

Purpose of the Study:

• To generalize the hybrid scheme for multireference methods.
• To introduce new hybrid methods by combining various theoretical approaches.
• To test a new excitation space separation strategy.

Main Methods:

• Generalization of the hybrid scheme for multireference methods.
• Development of new hybrid methods using internally contracted multireference coupled-cluster, unshifted multireference coupled electron pair, and multireference perturbation methods.
• Implementation of a new excitation space separation combining singles and doubles excitations into the external space.

Main Results:

• The generalized hybrid methods were derived and benchmarked.
• The new separation of excitation space was tested.
• Hybrid methods generally show improvement over their non-hybrid counterparts.

Conclusions:

• The developed hybrid methods offer a favorable balance between computational cost and accuracy.
• These methods provide a valuable tool for accurate electronic structure calculations.
• The generalization enhances the applicability of hybrid schemes in computational chemistry.