19.2 How to Use

As usual mpshift requires converged molecular orbitals from a dscf or ridft run. No specific open-shell keywords are needed for the orbital contribution $\bm{\sigma}^{\text{orb}}$. That is, the keywords for the closed-shell NMR shieldings are applied. The EPR properties are calculated as done in the previous section. All functionals up to the class of range-separated and local hybrids are supported [347]. The current-dependent generalization is strongly recommended for meta-GGAs-based functionals.

The $pnmr flag defines which terms will be included or at which temperature and for what spin the shielding will be calculated. Possible options are as follows.

followed by fc, sd, and/or psoso; The respective terms of the HFC tensor are included. Default are all terms (FC, SD, PSOSO).
followed by gelec; Avoids calculating the g-tensor by using the g-factor of the free electron. By default, mpshift calculates the g-tensor.
followed by g = real; Avoids calculating the g-tensor by using the g-factor of real. By default, mpshift calculates the g-tensor.
followed by none; Only calculate the orbital contribution, i.e. omit the g-tensor, HFC, and ZFS tensors.
followed by zfs; Calculate the total ZFS tensor. zfs-dip or zfs-soc only calculate the corresponding contributions. The dipolar term can be calculated directly with the unrestricted natural orbitals (UNOs) with uno, which is also the default, or directly with direct.
followed by spin = real; Uses a user-defined spin of as a prefactor instead of the expectation value of $\hat{S}_z$ calculated from the UHF/UKS occupation. By default the occupation defines the spin.
followed by temp = real; Define the temperature in Kelvin. By default, 298 K are assumed.

Taking together, by default all HFC terms are included and the g-tensor will be calculated. The pNMR shielding tensor is then calculated at 298 K with the effective spin from the $\alpha$ and $\beta$ occupation numbers. For doublet systems, this will yield the full pNMR shielding tensor, as the ZFS part is not needed explicitly.

For triplet systems and beyond, the ZFS part should be calculated additionally using $pnmr with zfs. Then, the option $printpnmr can be set to store all tensors on disk in the file pnmrshift.inp, which can be parsed by the PNMRShift program. mpshift will print a shielding tensor in the end of the output, which is calculated with the given spin and Eq. 19.1. This is, however, just an approximation and we strongly recommend to evaluate the proper expression with the PNMRShift program.