Geminal-spanning orbitals make explicitly correlated reduced-scaling coupled-cluster methods robust, yet simple.

Area of Science:

• Computational Chemistry
• Quantum Chemistry
• Method Development

Background:

• Accurate prediction of intermolecular interactions is crucial in chemistry and materials science.
• Explicitly correlated (F12) coupled-cluster methods offer high accuracy but are computationally expensive.
• Pair-natural orbitals (PNOs) can reduce the computational cost of high-level correlated methods.

Purpose of the Study:

• To implement a production-level, reduced-scaling explicitly correlated (F12) coupled-cluster singles and doubles (CCSD) method utilizing PNOs.
• To improve the efficiency and reduce the computational cost of F12-CCSD calculations.
• To assess the accuracy of the new method for weak intermolecular interactions.

Main Methods:

• Development of a reduced-scaling F12-CCSD method incorporating PNOs.
• Reformulation of explicitly correlated terms using geminal-spanning orbitals to minimize truncation errors.
• Application of the method to the S66 benchmark set for weak intermolecular interactions.

Main Results:

• The PNO-based F12-CCSD method achieves high accuracy, reproducing the complete basis set CCSD limit for interaction energies.
• Mean absolute errors for interaction energies on the S66 benchmark are less than 0.1 kcal/mol.
• Significant reduction in computational cost compared to conventional F12-CCSD methods.

Conclusions:

• The developed PNO-F12-CCSD method provides an accurate and computationally efficient approach for studying intermolecular interactions.
• The use of geminal-spanning orbitals effectively reduces errors associated with F12 contributions.
• This method offers a practical alternative for large-scale electronic structure calculations involving weak interactions.