Spin-Free [2]R12 Basis Set Incompleteness Correction to the Local Multireference Configuration Interaction and the...

Area of Science:

• Computational Chemistry
• Quantum Chemistry
• Theoretical Chemistry

Background:

• Local multireference methods like LMRCI and LMRACPF are crucial for accurate electronic structure calculations.
• Basis set incompleteness is a significant source of error in these calculations.
• Explicit correlation methods are needed to improve accuracy.

Purpose of the Study:

• To extend LMRCI and LMRACPF methods with explicit correlation using the [2]R12 correction.
• To evaluate the performance of these extended methods for calculating bond dissociation energies (BDEs).
• To assess the accuracy compared to conventional methods and different basis sets.

Main Methods:

• Incorporation of the universal spin-free [2]R12 basis set incompleteness correction into LMRCI and LMRACPF.
• Application of LMRCI+[2]R12 (with and without Davidson + Q correction) and LMRACPF+[2]R12 methods.
• Calculation of BDEs for ethene, perfluoroethene, propene, and 2-butene.

Main Results:

• The extended methods (LMRCI+[2]R12, LMRCI+Q+[2]R12, LMRACPF+[2]R12) yield BDEs comparable in accuracy to conventional methods using a basis set one cardinal number higher.
• The accuracy of BDEs computed with [2]R12 corrected methods is preserved when using smaller basis sets (June calendar) versus larger conventional aug-cc-pVXZ basis sets.
• The [2]R12 correction effectively mitigates basis set incompleteness errors.

Conclusions:

• The [2]R12 correction provides a computationally efficient way to achieve high accuracy in BDE calculations using local multireference methods.
• These extended methods offer a reliable approach for studying chemical reaction energetics, particularly bond dissociation.
• The findings suggest potential for significant computational savings without sacrificing accuracy.