Towards Near-Exact Solutions of Molecular Electronic Structure: Full Coupled-Cluster Reduction with a Second-Order...

Area of Science:

• Quantum Chemistry
• Computational Chemistry
• Theoretical Chemistry

Background:

• Accurate solutions to the electronic Schrödinger equation are crucial for understanding molecular properties.
• Full Coupled-Cluster Reduction (FCCR) offers a size-extensive approach by reducing excitation manifolds.
• Estimating residual correlation in FCCR remains a challenge for highly correlated systems.

Purpose of the Study:

• Introduce an augmented adaptation of FCCR, termed FCCR(2), incorporating a second-order perturbative correction.
• Enable accurate estimation of residual correlation energy within the FCCR framework.
• Achieve near-exact electronic energies for challenging molecular systems.

Main Methods:

• Developed FCCR(2) by adding a second-order perturbative correction (E(2)) to FCCR.
• Utilized the complementary space of the FCCR projection manifold for calculating E(2).
• Exploited the linear relationship between E(2) and FCCR(2) energy for accurate predictions.

Main Results:

• FCCR(2) accurately estimates residual correlation energy.
• Demonstrated near-exact ground-state electronic energies for benzene in various geometries.
• Accurately calculated the isomerization energy of the transition metal complex [Cu(NH3)]2O22+.

Conclusions:

• FCCR(2) provides a robust and accurate method for calculating electronic energies, especially for systems with strong electron correlation.
• The method shows significant potential for applications in computational chemistry and materials science.
• FCCR(2) advances the capability of coupled-cluster methods for complex molecular systems.