Coupled cluster-inspired geminal wavefunctions.

Area of Science:

• Quantum Chemistry
• Computational Chemistry
• Electronic Structure Theory

Background:

• Electron pairs, described by two-electron wavefunctions (geminals), are fundamental to chemical bonding and reactivity.
• Traditionally, single-particle methods have been dominant, limiting the widespread application of geminal-based approaches.
• A resurgence in geminal methods is driven by the need for accurate descriptions of strongly correlated phenomena.

Purpose of the Study:

• To develop accurate and computationally efficient geminal wavefunction methods.
• To extend the concept of one-reference orbitals to other geminals.
• To incorporate single-like excitations within a quasiparticle framework for improved accuracy.

Main Methods:

• Proposal of new geminal wavefunction families inspired by the pair coupled cluster doubles ansatz.
• Development of a hierarchy of two-electron wavefunctions extending the one-reference orbital concept.
• Incorporation of single-like excitations and exploration of seniority restrictions.

Main Results:

• Introduction of novel geminal wavefunction hierarchies.
• Demonstration of incorporating single-like excitations without compromising the quasiparticle picture.
• Benchmarking of new methods on model strongly correlated systems.

Conclusions:

• The proposed geminal methods offer a computationally tractable and accurate alternative to traditional single-particle approaches.
• These methods provide a promising avenue for studying complex molecules and materials with strong electron correlation.
• The developed framework facilitates the application of geminal wavefunctions in electronic structure calculations.