The Importance of the Density Functional Theory Exchange–Correlation Hartree–Fock Term in Magnetic Resonance: Application to an Aqueous Environment

Abstract

Within the framework of Density Functional Theory (DFT), the relevance of the term Hartree−Fock exchange (HFE) for a variety of molecular properties is a critical point. For this reason, we spend efforts to understand these relationships in nuclear magnetic resonance (NMR) parameters in a water solvent. This work takes advantage of the appropriate aug-cc-pVTZ-J basis set and the Minnesota family of DFT methods, which consider different portions of HFE contributions. With regard to solvent participation, the results are based on a sequential Monte Carlo/Quantum Mechanics procedure, which builds the structures of the liquid under realistic thermodynamic conditions. Compared to the accurate results of second-order polarization propagator approximation (SOPPA) and experimental data, all NMR parameters show a huge dependence on the size of the HFE contribution. For instance, the inclusion of this term in 1 J OH and 2 J HH indirect spin−spin couplings does vary with 49.661 and 25.459 Hz, respectively. The M06-HF method accounts for 100% of HFE and better matches the σ O and σ H shielding constants. On the other hand, 1 J OH and 2 J HH demand a medium contribution (54% of HFE), the best description being associated with the M06-2X method. Thus, the dependence varies regarding the phenomenology of the property in focus and the order for independent treatments. For elements that participate in hydrogen bonds simultaneously as donor and acceptor actors, the results indicate that explicit solvent molecules must be considered in the quantum mechanical calculations for better modeling of paramagnetic shielding constants.

Spin–Spin Coupling Constant Based on Reference Interaction Site Model Self-Consistent Field with Constrained Spatial Electron Density

“…4,5 It has been pointed out that, in addition to the effects of electron correlation, it is important to consider solvent effects, rovibrational effects, and relativistic effects. 4 In particular, the solvent effect is considered important because measurements are performed in solutions, and polar atoms such as 15 N, 17 O, and 19 F are susceptible to solvent effects including hydrogen bonding.…”

“…Although this method is expected to work well when the polarity of the solvent is not high, it is not effective in describing strong solvent effects such as hydrogen bonding. For this reason, solvation models have been developed that go beyond the simple continuum model. , Calculations using supermolecule methods , or simulation-based methods − have also been reported. Properly describing solvation phenomena with these methods requires increasing the number of solvent molecules and obtaining sufficient statistical sampling.…”

“…The experimental value of J OH in nitromethane- d 3 (−80.6 Hz) is represented by the black dashed line, which serves as the gas-phase reference . The experimental value of J OH in bulk water has also been obtained, and the solvent shift is estimated to be around −10 Hz in some studies. , However, due to controversies surrounding this result, the present study focuses on changes in solvent effects caused by PCM or RISM-SCF-cSED, rather than precisely calculating the experimental J OH in water. Similar to the results in Table , the coupling constants calculated using RISM-SCF-cSED are the lowest among all functionals tested.…”