Calculation of electronic g-tensors using coupled cluster theory

Area of Science:

• Quantum Chemistry
• Computational Chemistry
• Spectroscopy

Background:

• Accurate prediction of electronic g-tensors is crucial for understanding molecular properties and reaction mechanisms.
• Coupled cluster (CC) methods offer high accuracy but can be computationally demanding.
• Density functional theory (DFT) provides a computationally cheaper alternative, but its accuracy for g-tensors needs validation.

Purpose of the Study:

• To develop and present a computational scheme for calculating electronic g-tensors using coupled cluster (CC) theory.
• To investigate the impact of electron correlation and basis set convergence on g-tensor calculations.
• To benchmark DFT functionals against CC results for predicting g-tensors, particularly for radicals.

Main Methods:

• Implementation of an effective one-electron spin-orbit operator within a CC framework.
• Inclusion of arbitrary excitations in the cluster operator and options for orbital relaxation and reference determinants.
• Utilization of gauge-including atomic orbitals (GIAOs) to address the gauge origin problem.
• Benchmark calculations on the NH ((3)Sigma(-)) radical.

Main Results:

• Electron correlation effects are vital for accurate g-tensor prediction.
• Basis set convergence for g-tensor calculations is slow, with marginal improvement from GIAOs.
• CC singles and doubles (CCSD) results validate DFT functionals.
• The B3LYP hybrid functional demonstrated the best performance among tested DFT functionals for light-element radicals.

Conclusions:

• The presented CC scheme provides a robust method for accurate g-tensor calculations.
• Electron correlation plays a significant role in determining g-tensor values.
• B3LYP is recommended as a reliable DFT functional for g-tensor predictions of light-element radicals.