Simulating Spin-Orbit Coupling with Quasidegenerate N-Electron Valence Perturbation Theory

Area of Science:

• Quantum Chemistry
• Computational Chemistry
• Theoretical Chemistry

Background:

• Accurate theoretical treatment of electron correlation and spin-orbit coupling is crucial for understanding molecular properties.
• Existing methods often struggle to efficiently combine static and dynamic correlation with spin-orbit effects.

Purpose of the Study:

• To implement and validate spin-orbit coupling effects within the quasidegenerate N-electron valence perturbation theory (QDNEVPT2) framework.
• To assess the accuracy of the new SO-QDNEVPT2 and SOMF-QDNEVPT2 methods for various chemical systems.

Main Methods:

• Development of the first implementation of spin-orbit coupling in fully internally contracted second-order quasidegenerate N-electron valence perturbation theory (SO-QDNEVPT2).
• Inclusion of a simplified spin-orbit mean-field approximation (SOMF-QDNEVPT2).
• Application to group 14 and 16 hydrides, 3d and 4d transition metal ions, and actinide dioxides.

Main Results:

• SO-QDNEVPT2 and SOMF-QDNEVPT2 accurately predict zero-field splittings for group 14 and 16 molecules.
• SO-QDNEVPT2 shows significantly higher accuracy than SOMF-QDNEVPT2 for 3d transition metal ions.
• Both methods provide results in good agreement with experimental and previous theoretical data for transition metal ions and actinide dioxides.

Conclusions:

• SO-QDNEVPT2 and SOMF-QDNEVPT2 are effective multireference methods for incorporating spin-orbit coupling.
• These methods offer a computationally efficient approach for studying systems with strong spin-orbit interactions.
• The developed methods represent a significant advancement in computational quantum chemistry.