Gaussian 03 Online Manual
Last update: 13 February 2008
NMR
This properties keyword predicts NMR shielding tensors and magnetic susceptibilities using the Hartree-Fock method, all DFT methods and the MP2 method [232,234,528, 587].
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.
Spin-spin coupling constants may also be computed during an NMR job [238,239,240,241], via the SpinSpin option.
SpinSpin
Compute spin-spin coupling constants in addition to the usual NMR properties.
This calculation type has a computational cost of about twice that of computing
vibrational frequencies. It is available only for Hartree-Fock and DFT methods.
ReadAtoms
Calculate spin-spin coupling constants only for selected atoms. The input is a free format list terminated with a blank line. Ranges of atoms are also allowed (e.g., 7-12).
Mixed
Compute spin-spin coupling in two steps. In the first, the basis set specified by the user is modified to be appropriate for the Fermi Contact term, by uncontracting the basis and adding tight polarization functions for the core. In the second step, the other three terms in the spin-spin coupling are done with the standard basis. The final results reported at the end of the second job step include the Fermi Contact contribution from the first step. This significantly improves the accuracy of spin-spin coupling constants, especially when done with typical valence-oriented basis sets such as 6-31G** or Aug-CC-pVTZ.
CSGT
Compute NMR properties using the CSGT method only.
GIAO
Compute
NMR properties using the GIAO method only. This is the default.
IGAIM
Use atomic centers as gauge origins.
SingleOrigin
Use a single
gauge origin. This method is provided for comparison purposes but is not generally
recommended.
All
Compute properties with all three of the SingleOrigin,
IGAIM, and CSGT methods.
Display the eigenvectors of the shielding tensor for each atom
FCOnly
Compute only the Fermi contact spin-spin terms.
ReadFC
Read the Fermi contact spin-spin terms from the checkpoint file and then compute the other spin-spin coupling terms.
Susceptibility
Compute the magnetic susceptibility as well as the shielding.
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).