Perturbative triples correction for local pair natural orbital based explicitly correlated CCSD(F12*) using Laplace...

Area of Science:

• Computational Chemistry
• Quantum Chemistry
• Theoretical Chemistry

Background:

• Coupled cluster methods are essential for accurate electronic structure calculations.
• Pair natural orbital (PNO) approximations reduce computational cost for large systems.
• The perturbative triples correction (T) is crucial for high accuracy but computationally expensive.

Purpose of the Study:

• To implement and validate a pair natural orbital coupled cluster singles and doubles with perturbative triples (PNO-CCSD(T)) method.
• To avoid the quasi-canonical triples approximation (T0) by using a numerical Laplace transformation.
• To combine PNO-based triples with explicitly correlated methods like PNO-CCSD(F12*).

Main Methods:

• Implementation of PNO-CCSD(T) avoiding the T0 approximation.
• Numerical Laplace transformation for the perturbative (T) triples correction to mitigate I/O and storage bottlenecks.
• Combination with explicitly correlated PNO-CCSD(F12*) and investigation of specialized F12-PNOs.

Main Results:

• The numerical Laplace transformation requires few grid points for converged energy differences.
• PNO-CCSD(T) demonstrates improved robustness and reduced deviation from canonical CCSD(T) compared to PNO-CCSD(T0).
• PNO-CCSD(F12*)(T) can be applied as a black-box method without significant additional errors.

Conclusions:

• The developed PNO-CCSD(T) method offers a more accurate and efficient alternative to the T0 approximation.
• Laplace transformation is an effective strategy for handling triples amplitudes.
• The combination with explicitly correlated methods provides a robust and user-friendly approach for high-accuracy electronic structure calculations.