Gauge-origin dependence in electronic g-tensor calculations.

Area of Science:

• Quantum Chemistry
• Computational Spectroscopy
• Electronic Structure Theory

Background:

• The electronic g-tensor is crucial for understanding electron magnetic properties.
• Gauge-origin dependence in g-tensor calculations can introduce significant errors, especially for larger molecules.
• Previous studies highlight the limitations of common gauge-origin approaches in density functional theory (DFT) calculations.

Purpose of the Study:

• To benchmark the gauge-origin dependence of electronic g-tensor calculations.
• To evaluate the accuracy of common gauge-origin approaches for small and extended molecules.
• To propose and validate a new pragmatic ansatz for gauge-origin selection.

Main Methods:

• Unrestricted density functional theory (DFT) calculations.
• Spin-orbit mean field (SOMF) ansatz.
• Gauge-including atomic orbitals (GIAO) as a reference method.
• Analysis of spin density distribution to inform gauge-origin selection.

Main Results:

• Common gauge-origin calculations are accurate for small molecules but unreliable for extended systems.
• Errors from common gauge-origin approaches in larger molecules can exceed basis set errors.
• Accuracy depends on the locality of the spin density distribution.
• A new pragmatic ansatz shows reasonable accuracy for single localized spin centers.

Conclusions:

• Common gauge-origin methods are insufficient for consistently accurate g-tensor calculations in molecules with multiple, spatially distant spin centers.
• Distributed gauge-origin methods, such as GIAO, are the ideal approach for accurate g-tensor computation in larger molecular systems.
• The proposed pragmatic ansatz offers a practical improvement for specific cases but does not universally replace distributed methods.