A Local Pair Natural Orbital-Based Multireference Mukherjee's Coupled Cluster Method.

Area of Science:

• Computational Chemistry
• Quantum Chemistry
• Theoretical Chemistry

Background:

• Mukherjee's state-specific multireference coupled cluster (MkCC) method provides accurate electronic structure calculations.
• Traditional MkCC methods can be computationally expensive for large molecules.

Purpose of the Study:

• To develop and validate a computationally efficient local variant of the MkCC method.
• To assess the accuracy of the new method for calculating relative energies and correlation energy.

Main Methods:

• Development of a local pair natural orbital variant of Mukherjee's coupled cluster method (LPNO-MkCC).
• Implementation restricted to single and double excitations (LPNO-MkCCSD).
• Testing on naphthyne isomers, tetramethyleneethane, and β-carotene using the ORCA program.

Main Results:

• LPNO-MkCCSD recovered 99.7-99.8% of the correlation energy compared to the canonical MkCC method.
• Errors in relative energies were below 0.4 kcal/mol, achieving chemical accuracy.
• Efficient computation of a large molecule (β-carotene) on a single CPU core was demonstrated.

Conclusions:

• The LPNO-MkCCSD method offers a significant speed-up with minimal loss of accuracy.
• This approach enables accurate electronic structure calculations for larger and more complex molecular systems.
• The developed method is a valuable tool for theoretical and computational chemistry research.