10.11.1 Introduction

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. ¹⁰¹³ Ochsenfeld C.
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Since the Q-Chem 7.0 release, the new finite difference (FD) based NMR shielding calculation is avaliable. When using finite difference on analytic first derivative (FD1), the FD1-NMR shielding calculation is much more efficient than the fully analytic implementation due to the support of efficient GIAO based RI-JK and occ-RI-K algorithms (avaliable for global hybrid and range-separated functionals), and better parallelization. Together with the efficiency improvements, the FD-NMR feature also supports GDM and basis functions of higher angular momentum.

Features of Q-Chem’s analyticNMR package include:

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

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

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

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  DIIS acceleration.

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  Support for basis sets up to $h$ functions.

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  Support for LDA, GGA, Meta-GGA, ⁹²³ Maximoff S. N., Scuseria G. E.
  Chem. Phys. Lett.
  (2004), 390, pp. 408. Link global hybrid and common range-separated functionals (RSH only support s, p and d basis functions). VV10 is the only non-local correlation functional supported.

Calculation of NMR chemical shifts and indirect spin-spin couplings is discussed in Section 10.11.2. Additional magnetic properties can be computed, as described in Section 10.11.4. These include hyperfine interaction tensors (electron spin–nuclear spin interaction) and nuclear quadrupole interactions with electric field gradients.