Local Wave Function Embedding: Correlation Regions in PNO-LCCSD(T)-F12 Calculations.

Area of Science:

• Computational Chemistry
• Quantum Chemistry
• Chemical Physics

Background:

• Chemical reactions often involve localized changes, leaving most molecular structures intact.
• Accurate computation of reaction energies is crucial but computationally expensive for large systems.

Purpose of the Study:

• To extend the region method for accurate calculation of reaction energies in large molecular systems.
• To investigate the efficiency and accuracy of correlating only electrons near the reaction center.

Main Methods:

• Extension of the region method to the PNO-LCCSD(T)-F12 quantum chemical method.
• Selective electron correlation: high-level (PNO-LCCSD(T)-F12) in a localized region, lower-level (PNO-LMP2-F12) or uncorrelated (Hartree-Fock frozen core) elsewhere.
• Application to reaction energy calculations and spin-state energy differences in transition metal complexes.

Main Results:

• Computed reaction energies converge rapidly with the size of the localized correlation region.
• Including 2-3 bonds around reacting atoms reproduces full calculation results within ±0.2 kcal/mol.
• A factor of 15 in computation time was saved for a transition metal complex, with accuracy within ±0.1 kcal/mol of full calculation.

Conclusions:

• The region method effectively reduces computational cost for accurate reaction energy calculations.
• Localized electron correlation provides a computationally efficient pathway to high accuracy for large molecular systems.
• This approach is applicable to diverse chemical problems, including spin-state energetics in transition metal complexes.