Electric Field Gradients Calculated from Two-Component Hybrid Density Functional Theory Including Spin-Orbit Coupling

Area of Science:

• Computational Chemistry
• Quantum Chemistry
• Relativistic Quantum Chemistry

Background:

• Nuclear electric field gradients (EFGs) are crucial for understanding molecular electronic structure and chemical bonding.
• Accurate calculation of EFGs, especially for heavy elements, requires relativistic quantum chemical methods.
• Existing methods may not fully capture the complexities of relativistic effects on EFGs.

Purpose of the Study:

• To implement and report a four-component density-corrected approach for calculating molecular EFGs.
• To enable scalar and spin-orbit relativistic computations of EFGs within the NWChem package.
• To benchmark the new method using density functional calculations across various molecular systems.

Main Methods:

• Implementation of a four-component density-corrected approach.
• Utilizing the two-component relativistic zeroth-order regular approximation (ZORA).
• Performing benchmark density functional calculations with various functionals (nonhybrid, hybrid).

Main Results:

• Calculations were performed on main group diatomics, Cu/Au diatomics, Ru/Nb complexes, and uranyl species.
• Comparison of results from nonhybrid and hybrid functionals provided insights into their performance.
• Localized molecular orbital (LMO) decomposition offered chemically intuitive interpretations of EFGs.

Conclusions:

• The implemented method provides accurate EFGs, particularly highlighting the role of valence d and f shells in heavy elements.
• LMO analysis, aided by a Townes-Dailey-like model for f orbitals, simplifies the interpretation of complex electronic structures.
• This approach enhances the understanding of chemical bonding and electronic properties in relativistic systems.