Benchmarking NMR indirect nuclear spin-spin coupling constants: SOPPA, SOPPA(CC2), and SOPPA(CCSD) versus CCSD

Area of Science:

• Computational Chemistry
• Quantum Chemistry
• Spectroscopy

Background:

• Accurate calculation of NMR indirect nuclear spin-spin coupling constants is crucial in chemistry.
• Existing high-accuracy methods like CCSD and SOPPA(CCSD) have a high computational cost (N^6 scaling).
• This computational expense limits their application to small molecules (10-15 non-hydrogen atoms).

Purpose of the Study:

• To develop a more computationally efficient method for calculating spin-spin coupling constants.
• To introduce the SOPPA(CC2) method as a faster alternative to SOPPA(CCSD).
• To assess the performance and accuracy of SOPPA(CC2) compared to existing methods.

Main Methods:

• Development of the SOPPA(CC2) method, replacing CCSD amplitudes with CC2 amplitudes in SOPPA(CCSD).
• Comparison of SOPPA(CC2) performance against SOPPA and SOPPA(CCSD) using benchmark molecules.
• Investigation of basis set dependence using HuzIV-su4, ccJ-pVTZ, and ccJ-pVQZ basis sets.

Main Results:

• The new SOPPA(CC2) method exhibits N^5 scaling, significantly improving computational efficiency.
• SOPPA(CC2) demonstrates comparable accuracy to SOPPA(CCSD) for calculating spin-spin coupling constants.
• Basis set choice influences the accuracy of the calculated coupling constants.

Conclusions:

• SOPPA(CC2) provides a computationally feasible approach for routine calculation of NMR spin-spin coupling constants.
• This method extends the applicability of accurate calculations to larger and more complex molecular systems.
• The developed method balances accuracy and computational cost effectively.