Universal state-selective corrections to multi-reference coupled-cluster theories with single and double excitations

Area of Science:

• Quantum Chemistry
• Computational Chemistry
• Theoretical Chemistry

Background:

• Approximate multi-reference coupled-cluster (MRCC) methods are essential for accurate electronic structure calculations.
• Universal state-selective (USS) corrections offer a general approach to enhance the accuracy of MRCC energies.
• The Jeziorski-Monkhorst exponential ansatz forms the basis for many MRCC theories.

Purpose of the Study:

• To evaluate the performance of a simple universal state-selective (USS) correction applied to Brillouin-Wigner (BW) and Mukherjee (Mk) MRCC methods.
• To assess the accuracy of USS-corrected Brillouin-Wigner single and double excitations (USS-BW-MRCCSD) and USS-corrected Mukherjee single and double excitations (USS-Mk-MRCCSD) against full configuration interaction (FCI) benchmarks.
• To explore the relationship between USS-BW-MRCCSD and existing a posteriori corrections in BW-MRCCSD calculations.

Main Methods:

• Implementation and application of USS corrections to Brillouin-Wigner (BW) and Mukherjee (Mk) MRCC theories.
• Utilized single and double excitations within the MRCC frameworks.
• Performed benchmark calculations comparing USS-BW-MRCCSD and USS-Mk-MRCCSD results with full configuration interaction (FCI) data.

Main Results:

• The USS correction is applicable to various MRCC theories based on the Jeziorski-Monkhorst ansatz.
• USS-BW-MRCCSD results demonstrate a connection to established a posteriori corrections in BW-MRCCSD.
• Both USS-BW-MRCCSD and USS-Mk-MRCCSD show good agreement with full configuration interaction (FCI) results in benchmark calculations.

Conclusions:

• The evaluated USS corrections provide a valuable and broadly applicable method for improving the accuracy of approximate MRCC energies.
• USS-corrected MRCC methods, specifically USS-BW-MRCCSD and USS-Mk-MRCCSD, offer a computationally feasible route to near-FCI accuracy for challenging electronic systems.
• The findings support the utility of USS corrections in advancing the capabilities of quantum chemical calculations.