Gaussian 03 Online Manual
NMR shielding tensors may be computed with the Continuous Set of Gauge Transformations (CSGT) method [231,233,235] and the Gauge-Independent Atomic Orbital (GIAO) method [226,227,228,229,230]. Magnetic susceptibilities may also be computed with both GIAOs [236,237] and CGST. Gaussian also supports the IGAIM method [231,233] (a slight variation on the CSGT method) and the Single Origin method, for both shielding tensor and magnetic susceptibilities.
Structures used for NMR calculations should have been optimized at a good level of theory. Note that CSGT calculations require large basis sets to achieve accurate results.
SCF, DFT and MP2 methods. In Gaussian 03, NMR may be combined with SCRF.
Here is an example of the default output from NMR:
Magnetic properties (GIAO method) Magnetic shielding (ppm): 1 C Isotropic = 57.7345 Anisotropy = 194.4092 XX= 48.4143 YX= .0000 ZX= .0000 XY= .0000 YY= -62.5514 ZY= .0000 XZ= .0000 YZ= .0000 ZZ= 187.3406 2 H Isotropic = 23.9397 Anisotropy = 5.2745 XX= 27.3287 YX= .0000 ZX= .0000 XY= .0000 YY= 24.0670 ZY= .0000 XZ= .0000 YZ= .0000 ZZ= 20.4233
For this molecular system, the values for all of the atoms of a given type are equal, so we have truncated the output after the first two atoms.
The additional output from spin-spin coupling computations appears as follows:
Total nuclear spin-spin coupling K (Hz): 1 2 1 0.000000D+00 2 0.147308D+02 0.000000D+00 Total nuclear spin-spin coupling J (Hz): 1 2 1 0.000000D+00 2 0.432614D+03 0.000000D+00
The various components of the coupling constants precede this section in the output file. It displays the matrix of isotropic spin-spin coupling between pairs of atoms in lower triangular form. The K matrix gives the values which are isotope-independant, and the J matrix gives the values taking the job's specific isotopes into account (whether explicitly specifed or the default isotopes).