Indirect nuclear spin-spin couplings with third-order contributions added to the SOPPA method

Area of Science:

• Computational chemistry
• Quantum chemistry
• Theoretical chemistry

Background:

• Indirect nuclear spin-spin couplings are crucial molecular properties.
• Standard second-order polarization propagator approximation (SOPPA) is computationally efficient but less accurate than coupled cluster methods.
• Coupled cluster methods provide high accuracy but are computationally expensive.

Purpose of the Study:

• To introduce and evaluate a modified SOPPA method (SOPPA+A3-3) for calculating indirect nuclear spin-spin couplings.
• To enhance the accuracy of SOPPA by incorporating third-order terms.
• To assess the performance and computational cost of the new method compared to standard SOPPA and coupled cluster methods.

Main Methods:

• Development of the SOPPA+A3-3 method by adding specific third-order A matrix terms to the standard SOPPA.
• Calculation of spin-spin couplings for various molecules using SOPPA+A3-3.
• Comparison of SOPPA+A3-3 results with those from standard SOPPA and coupled cluster singles and doubles (CCSD) methods.
• Utilizing the Dalton program for implementation.

Main Results:

• The SOPPA+A3-3 method yields more accurate spin-spin coupling constants than the standard SOPPA method.
• The accuracy achieved by SOPPA+A3-3 is comparable to that of CCSD methods.
• The increase in computational cost for the response calculation is minimal, especially for small to medium-sized molecules.

Conclusions:

• The SOPPA+A3-3 method represents a significant improvement over standard SOPPA for calculating indirect nuclear spin-spin couplings.
• This modified method offers a favorable balance between accuracy and computational cost.
• The implementation in the Dalton program demonstrates the practical utility of these third-order contributions.