Reliable Isotropic Electron-Paramagnetic-Resonance Hyperfine Coupling Constants from the Frozen-Density Embedding...

Area of Science:

• Computational Chemistry
• Quantum Chemistry
• Spectroscopy

Background:

• Accurate calculation of hyperfine coupling constants is crucial for understanding radical species.
• Existing methods like Kohn-Sham density-functional theory (KS-DFT) and frozen-density embedding (FDE) have limitations in accuracy and computational cost.
• The S22 test set provides a standard benchmark for evaluating computational methods for molecular interactions.

Purpose of the Study:

• To systematically benchmark the performance of the frozen-density embedding quasi-diabatization (FDE-diab) approach for calculating isotropic electron-paramagnetic-resonance hyperfine coupling constants.
• To compare FDE-diab with Kohn-Sham density-functional theory (KS-DFT) and standard frozen-density embedding (FDE).
• To assess the accuracy and computational efficiency of FDE-diab for both radical cations and anions.

Main Methods:

• Calculation of isotropic hyperfine coupling constants using the FDE-diab approach.
• Benchmarking against domain-based local pair natural orbital coupled cluster singles and doubles (DLPNO-CCSD(T)) as a reference.
• Comparison with results from KS-DFT and standard FDE.

Main Results:

• FDE-diab consistently outperforms standard FDE for both radical cations and anions.
• FDE-diab achieves reliable hyperfine couplings for radical cations using simpler generalized gradient approximation (GGA) functionals.
• For radical anions, FDE-diab provides accuracy comparable to KS-DFT.
• FDE-diab demonstrates significant computational advantages, particularly for larger systems like a π-stacked benzene octamer radical cation.

Conclusions:

• FDE-diab is a promising and accurate method for calculating hyperfine coupling constants in radical ions.
• The method offers a good balance between accuracy and computational cost, especially for radical cations.
• FDE-diab represents a valuable advancement in computational chemistry for studying paramagnetic species.