Vibrational Corrections to NMR Spin-Spin Coupling Constants from Relativistic Four-Component DFT Calculations

Area of Science:

• Quantum Chemistry
• Relativistic Quantum Mechanics
• Computational Chemistry

Background:

• Nuclear spin-spin coupling constants are crucial for molecular structure determination.
• Zero-point vibrational (ZPV) corrections account for molecular motion at absolute zero.
• Relativistic effects become significant for molecules containing heavy elements.

Purpose of the Study:

• To investigate the influence of relativistic effects on ZPV corrections to nuclear spin-spin coupling constants.
• To compare relativistic and nonrelativistic computational approaches for these corrections.
• To assess the accuracy of nonrelativistic approximations for ZPV corrections.

Main Methods:

• Utilized four-component Dirac-Kohn-Sham Density Functional Theory (DFT).
• Calculated ZPV corrections for various hydrides (H2X, XH3, XH4) and HC≡CPbH3.
• Compared results from relativistic and nonrelativistic calculations.

Main Results:

• Relativistic effects on ZPV corrections are more pronounced for lighter elements (Se, Ge) than for the coupling constants themselves.
• For heavier elements (Bi, Pb), relativistic effects are crucial, and nonrelativistic approximations lead to significant errors.
• Nonrelativistic ZPV corrections can be less accurate than omitting ZPV corrections entirely for heavy elements.

Conclusions:

• Relativistic calculations are essential for accurate ZPV corrections to spin-spin coupling constants, particularly for heavy elements.
• Nonrelativistic approximations for ZPV corrections can be misleading for molecules with heavy atoms.
• The study highlights the importance of incorporating relativistic effects in computational chemistry for precise predictions.