10 Molecular Properties and Analysis

10.12 NMR and Other Magnetic Properties

The importance of nuclear magnetic resonance (NMR) spectroscopy for modern chemistry and biochemistry cannot be overestimated. Since there is no direct relationship between the measured NMR signals and structural properties, the necessity for a reliable method to predict NMR chemical shifts arises and despite tremendous progress in experimental techniques, the understanding and reliable assignment of observed experimental spectra remains often a highly difficult task. As such, quantum chemical methods can be extremely useful, both in solution and in the solid state.706, 700, 108, 702, 703

Features of Q-Chem’s NMR package include:

  • Restricted Hartree-Fock and DFT calculations of NMR chemical shifts using gauge-including atomic orbitals.

  • Support of linear-scaling CFMM and LinK procedures (Section 4.6) to evaluate Coulomb- and exchange-like matrices.

  • Density matrix-based coupled-perturbed SCF approach for linear-scaling NMR calculations.

  • DIIS acceleration.

  • Support for basis sets up to h functions.

  • Support for LDA, GGA, and global hybrid functionals. Meta-GGA and range-separated functionals are not yet supported, nor are functionals that contain non-local correlation (e.g., those containing VV10).

Calculation of NMR chemical shifts and indirect spin-spin couplings is discussed in Section 10.12.1. Additional magnetic properties can be computed, as described in Section 10.12.3. These include hyperfine interaction tensors (electron spin–nuclear spin interaction) and nuclear quadrupole interactions with electric field gradients.