Description
This properties keyword predicts NMR shielding tensors and magnetic susceptibilities using the Hartree-Fock method, all DFT methods and the MP2 method [ Gauss92 J. Gauss, “Calculation of NMR chemical shifts at second-order many-body perturbation theory using gauge-including atomic orbitals,” Chem. Phys. Lett., 191 (1992) 614-20. DOI: , Gauss93 J. Gauss, “Effects of Electron Correlation in the Calculation of Nuclear- Magnetic-Resonance Chemical-Shifts,” J. Chem. Phys., 99 (1993) 3629-43. DOI: , Gauss95 J. Gauss, “Accurate Calculation of NMR Chemical-Shifts,” Phys. Chem. Chem. Phys., 99 (1995) 1001-08. DOI: , Cheeseman96 J. R. Cheeseman, G. W. Trucks, T. A. Keith, and M. J. Frisch, “A Comparison of Models for Calculating Nuclear Magnetic Resonance Shielding Tensors,” J. Chem. Phys., 104 (1996) 5497-509. DOI: ].
NMR shielding tensors may be computed with the Continuous Set of Gauge Transformations (CSGT) method [ Keith92 T. A. Keith and R. F. W. Bader, “Calculation of magnetic response properties using atoms in molecules,” Chem. Phys. Lett., 194 (1992) 1-8. DOI: , Keith93 T. A. Keith and R. F. W. Bader, “Calculation of magnetic response properties using a continuous set of gauge transformations,” Chem. Phys. Lett., 210 (1993) 223-31. DOI: , Cheeseman96 J. R. Cheeseman, G. W. Trucks, T. A. Keith, and M. J. Frisch, “A Comparison of Models for Calculating Nuclear Magnetic Resonance Shielding Tensors,” J. Chem. Phys., 104 (1996) 5497-509. DOI: ] and the Gauge-Independent Atomic Orbital (GIAO) method [ London37 F. London, “The quantic theory of inter-atomic currents in aromatic combinations,” J. Phys. Radium, 8 (1937) 397-409. DOI: , McWeeny62 R. McWeeny, “Perturbation Theory for Fock-Dirac Density Matrix,” Phys. Rev., 126 (1962) 1028. DOI: , Ditchfield74 R. Ditchfield, “Self-consistent perturbation theory of diamagnetism. 1. Gauge-invariant LCAO method for N.M.R. chemical shifts,” Mol. Phys., 27 (1974) 789-807. DOI: , Wolinski90 K. Wolinski, J. F. Hilton, and P. Pulay, “Efficient Implementation of the Gauge-Independent Atomic Orbital Method for NMR Chemical Shift Calculations,” J. Am. Chem. Soc., 112 (1990) 8251-60. DOI: , Cheeseman96 J. R. Cheeseman, G. W. Trucks, T. A. Keith, and M. J. Frisch, “A Comparison of Models for Calculating Nuclear Magnetic Resonance Shielding Tensors,” J. Chem. Phys., 104 (1996) 5497-509. DOI: ]. Magnetic susceptibilities may also be computed with both GIAOs [ Ruud93 K. Ruud, T. Helgaker, K. L. Bak, P. Jørgensen, and H. J. A. Jensen, “Hartree-Fock Limit Magnetizabilities from London Orbitals,” J. Chem. Phys., 99 (1993) 3847-59. DOI: ] and CGST. Gaussian also supports the IGAIM method [ Keith92 T. A. Keith and R. F. W. Bader, “Calculation of magnetic response properties using atoms in molecules,” Chem. Phys. Lett., 194 (1992) 1-8. DOI: , Keith93 T. A. Keith and R. F. W. Bader, “Calculation of magnetic response properties using a continuous set of gauge transformations,” Chem. Phys. Lett., 210 (1993) 223-31. DOI: ] (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 [ Helgaker00 T. Helgaker, M. Watson, and N. C. Handy, “Analytical calculation of nuclear magnetic resonance indirect spin-spin coupling constants at the generalized gradient approximation and hybrid levels of density-functional theory,” J. Chem. Phys., 113 (2000) 9402-09. DOI: , Sychrovsky00 V. Sychrovsky, J. Gräfenstein, and D. Cremer, “Nuclear magnetic resonance spin-spin coupling constants from coupled perturbed density functional theory,” J. Chem. Phys., 113 (2000) 3530-47. DOI: , Barone02 V. Barone, J. E. Peralta, R. H. Contreras, and J. P. Snyder, “DFT Calculation of NMR JFF Spin-Spin Coupling Constants in Fluorinated Pyridines,” J. Phys. Chem. A, 106 (2002) 5607-12. DOI: , Peralta03 J. E. Peralta, G. E. Scuseria, J. R. Cheeseman, and M. J. Frisch, “Basis set dependence of NMR Spin-Spin Couplings in Density Functional Theory Calculations: First row and hydrogen atoms,” Chem. Phys. Lett., 375 (2003) 452-58. DOI: , Deng06 W. Deng, J. R. Cheeseman, and M. J. Frisch, “Calculation of Nuclear Spin-Spin Coupling Constants of Molecules with First and Second Row Atoms in Study of Basis Set Dependence,” J. Chem. Theory and Comput., 2 (2006) 1028-37. DOI: ], via the SpinSpin option.
オプション
Options
SpinSpin
Compute spin-spin coupling constants in addition to the usual NMR properties. Be aware that this calculation type has a computational cost of about twice that of computing vibrational frequencies alone. It is available only for Hartree-Fock and DFT methods.
Mixed
Requests a two-step spin-spin coupling calculation [ Deng06 W. Deng, J. R. Cheeseman, and M. J. Frisch, “Calculation of Nuclear Spin-Spin Coupling Constants of Molecules with First and Second Row Atoms in Study of Basis Set Dependence,” J. Chem. Theory and Comput., 2 (2006) 1028-37. DOI: ]. This option causes two job steps to be run. 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 calculated with the unmodified basis set specified in the route section. 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 6-311G+(d,p), aug-CC-pVDZ or aug-CC-pVTZ. This approach is also faster than computing all four terms using a modified basis set incorporating tight polarization functions.
ReadAtoms
Calculate spin-spin coupling constants only for selected atoms. The atom list is specified in a separate input section (terminated by a blank line). The list is initially empty.
The input section uses the following format:
atoms=list [notatoms=list]
where each list is a comma or space-separated list of atom numbers, atom number ranges and/or atom types. Keywords are applied in succession. Here are some examples:
| atoms=3-6,17 notatoms=5 | Adds atoms 3, 4, 6 and 17 to the atom list. Removes 5 if present. |
| atoms=3 C 18-30 notatoms=H | Adds all C atoms and all non-H among atoms 3, 18-30. |
| atoms=C N notatoms=5 | Adds all C and N atoms except atom 5. |
| atoms=1-5 notatoms=H atoms=8-10 | Adds atoms 8-10 and non-hydrogens among atoms 1-5. |
Bare integers without a keyword are interpreted as atom numbers:
| 1,3,5 7 | Adds atoms 1, 3, 5 and 7. |
CSGT
Compute NMR properties using the CSGT method only. The data file for the ACID program can be generated with NMR=CSGT IOp(10/93=1).
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.
PrintEigenvectors
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.
適用範囲
Availability
SCF, DFT and MP2 methods. NMR may be combined with SCRF. NMR and Freq can now both be on the same route for HF and DFT.
実例
Examples
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-independent, and the J matrix gives the values taking the job’s specific isotopes into account (whether explicitly specified or the default isotopes).