*GIAOs*

It is strongly recommended to use GIAOs in the calculation of magnetic properties

*Large-scale calculations*

In large-scale calculations, it is recommended to treat the magnetic-field perturbations in
a sequential mode (keyword: **TREAT_PERTURBATION=SEQUENTIAL**) in order to reduce disk-space
requirements (storage of one set of perturbed two-electron integrals instead of simultaneous
storage of all perturbed two-electron integrals). In addition, partial
AO algorithms (keyword **ABCDTYPE=AOBASIS**) and the module *xecc* (keyword: **CC_PROG=ECC**)
should be used whenever possible.

**CC_PROG=ECC** is mandatory for NMR chemical shift calculations at CCSDT-n, CC3 and CCSDT level.

*Frozen-core calculations*

**Frozen-core orbitals** (i.e., frozen inner-shell orbitals) can be used within all
NMR chemical shift calculations.

*Files CSHIFT and CSHIFTSCF*

Files *CSHIFT* and *CSHIFTSCF* contain the corresponding shielding tensors as obtained at
HF-SCF and correlated levels, respectivey.

*Relative chemical shifts*

**Relative shifts** {$\delta$} are obtained via {$\delta = \sigma_{ref} - \sigma$} with {$\sigma_{ref}$} and {$\sigma$} as the isotropic shieldings of the chosen **reference compound** (e.g., TMS for 1H and 13C) and the nucleus of interest. Note that the calculation for the reference compound should be performed at the **same computational level (method, basis set, and geometry)** as for the actual compound of interest.

*Nuclear spin-rotation constants*

Additional calculation of **nuclear spin-rotation tensors** is invoked via the keyword
**SPIN_ROTATION=ON**

*Magnetizabilities and rotational g-tensors*

Additional calculation of **magnetizabilities** and **rotational g-tensors** is invoked via the
keyword **PROP=MAGNETIC** instead of **PROP=NMR**.

*Magnetically induced current densities*

Magnetically induced current densities can be computed after a NMR chemical-shift calculation using the
program **GIMIC** (not included in the standard release of CFOUR, see interface to *GIMIC*).