Hartree-Fock and density functional complete basis-set (CBS) predicted nuclear shielding anisotropy and shielding...

Area of Science:

• Computational Chemistry
• Quantum Chemistry
• Nuclear Magnetic Resonance (NMR) Spectroscopy

Background:

• Accurate calculation of nuclear shielding parameters is crucial for interpreting NMR spectra.
• Density functional theory (DFT) and Hartree-Fock methods are widely used for electronic structure calculations.
• Extrapolation to the complete basis-set (CBS) limit is often necessary for high accuracy.

Purpose of the Study:

• To calculate nuclear shielding anisotropy and shielding tensor components for a model set of molecules (N2, NH3, CH4, C2H4, HCN, CH3CN).
• To evaluate the accuracy of hybrid density functional (B3PW91) and Hartree-Fock methods in predicting these parameters.
• To assess the utility of a limited complete basis-set (CBS) extrapolation approach.

Main Methods:

• Hybrid density functional (B3PW91) and Hartree-Fock calculations were performed.
• A series of basis sets (cc-pVxZ and aug-cc-pVxZ, x=D, T, Q, 5, 6) were employed.
• Complete basis-set (CBS) limit parameters were estimated using 2- and 3-point fits.

Main Results:

• Calculated nuclear shielding anisotropies and tensor components for the model compounds were obtained.
• Both DFT and Hartree-Fock predicted CBS shielding parameters showed reasonable agreement with experimental data.
• The study demonstrated the feasibility of using a limited CBS approach for accurate calculations.

Conclusions:

• The B3PW91 functional and Hartree-Fock methods, when extrapolated to the CBS limit, provide reliable nuclear shielding parameters.
• A limited CBS approach is proposed as a complementary method for calculating anisotropic shielding parameters in larger molecules.
• This computational strategy can aid in the interpretation of solid-state NMR data for complex systems.