Keyword

Options:

NICS | Calculation of nuclear-independent chemical shifts. | ||

READ | Specifies that a list of nuclei for shielding tensor calculations is read from the keyword body of NMR. | ||

SPINROT | Calculation of the Nuclear Spin-Rotation Constants (NSRC). |

The magnetic shielding tensors can be calculated either within the AUXIS or BASIS GIAO formalism [255]. One or the other formalism is activated by the AUXIS or BASIS options of the VXCTYPE keyword. The GIAO scheme implemented thereby can be combined with ECPs and MCPs on neighboring centers in order to include scalar relativistic effects in the magnetic shielding tensor calculation. The default output only shows the calculated isotropic magnetic shielding [ppm] of each nucleus in the system:

(28) |

NMR READ H SYMMETRY ON BASIS (IGLO-III) VXCTYPE BASIS PBE # GEOMETRY Z-MATRIX ANGSTROM N H1 1 rNH H2 1 rNH 2 aHNH H3 1 rNH 3 aHNH 2 wHHNH # VARIABLES rNH 1.01700 aHNH 107.80000 wHHNH 120.00000

The NICS option of the NMR keyword [256] activates shielding tensor
calculations at the position of dummy atoms as specified in the keyword body
of the GEOMETRY keyword. The following input example enables NICS
calculations at two different positions, specified by `X1` and `X2`,
in an Al cluster.

NMR NICS READ X1 X2 CHARGE -2 PRINT NMR BASIS (DZVP) VXCTYPE BLYP AUXIS (GEN-A2) SCFTYP TOL=1.E-8 CDF=1.E-5 # GEOMETRY Z-MATRIX ANGSTROM X1 Al 1 AlX2 Al 1 AlX3 2 AlXAl3 Al 1 AlX4 2 AlXAl4 3 DIH4 Al 1 AlX5 3 AlXAl5 2 DIH5 X2 1 1.25 2 90.0 3 90.0 # VARIABLES AlX2 1.831000 AlX3 1.831000 AlX4 1.831000 AlX5 1.831000 AlXAl3 90.000000 AlXAl4 90.000000 AlXAl5 90.000000 DIH4 180.000000 DIH5 180.000000

The simulation of the magnetic shieldings along a BOMD trajectory is calculated in two steps as discussed in Section 4.7.3. A BOMD magnetic shielding calculation is activated by the option NMR=Integer of the simulation keyword (see 4.7.3). Here Integer specifies the number of the atom for which the trajectory data are printed. The user can select the nuclei by activating the option READ of the NMR keyword (see 4.8.8), otherwise the magnetic shielding of all nuclei will be calculated along the BOMD trajectory. In the following example, the magnetic shielding of the carbon nucleus of methanol along a BOMD trajectory is calculated as:

TITLE METHANOL MD SIMULATION # NMR READ C BASIS (AUG-CC-PVDZ) VXCTYPE AUXIS PW91 TRAJECTORY RESTART PART=10000-110000 SIMULATE CALCULATE NMR=1 INT=25 # GEOMETRY Z-MATRIX C H 1 HC2 H 1 HC3 2 HCH3 H 1 HC4 3 HCH4 2 DIH4 O 1 OC5 3 OCH5 2 DIH5 H 5 HO6 1 HOC6 3 DIH6 VARIABLES HC2 1.098100 HC3 1.098100 HCH3 109.120 HC4 1.098100 HCH4 109.120 DIH4 120.000 OC5 1.429200 OCH5 109.471 DIH5 240.000 HO6 0.975100 HOC6 107.690 DIH6 180.000 END

At the end of the corresponding output, the average and the standard deviation of the isotropic magnetic shieldings of all selected nuclei are printed.

The SPINROT option activates the computation of the NSRC for all magnetically active
nuclei in the molecule [257]. For the NSRC, it is necessary to indicate the
isotopic composition of the molecule which can be specified by the nuclear masses in
the GEOMETRY definition. The NSR tensor is evaluated in the principal axes of the
tensor of inertia. The output gives the values of the diagonal elements of the NSR
tensor, , and which are associated with the moments of
inertia arranged in the order . The components
are labeled A, B and C. Also the isotropic and anisotropic NSRC are given in the
output. The isotropic NSRC is calculated as:

(29) |

(30) |

DISPERSION BASIS (AUG-CC-PVDZ) AUXIS (GEN-A2) SCFTYPE MAX=1000 TOL=0.100E-04 VXCTYPE OPTX-PBE AUXIS TRAJECTORY RESTART PART=10000-12000 INT=20 NMR SPINROT SIMULATION CALCULATE NMR=1 INT=20 # # Cartesian coordinates of MD step 410000 # GEOMETRY CARTESIAN ANGSTROM F -66.916797 19.630729 -13.088069 18.998 H -67.101518 18.720636 -12.997091 2.014 C 54.166066 -15.936748 9.958016 12.000 C 53.957601 -15.619981 11.173715 12.000 H 54.766661 -16.089846 9.024499 1.008 H 53.312450 -15.623649 12.049412 1.008

In the output,

NSR CONSTANTS [kHz] FOR ATOM 1 TIME [FS] XX YY ZZ C_K <C_K> 5000.0 1.82 2.33 2.06 2.07 2.07 5010.0 2.76 1.91 1.87 2.18 2.12 5020.0 2.42 1.60 1.71 1.91 2.05 5030.0 1.63 1.77 1.90 1.77 1.98 5040.0 0.61 2.30 2.33 1.75 1.93 5050.0 0.04 2.87 2.83 1.91 1.93 5060.0 1.23 3.17 3.30 2.57 2.02 5070.0 2.32 2.91 3.31 2.85 2.12 5080.0 1.71 2.69 3.23 2.54 2.17 : : : : : : *** NMR SHIELDINGS STATISTIC *** CHEMICAL SHIELDING FOR ATOM 1 ( F ) AVERAGE SHIELDING [ppm] = 380.82 STD DEV SHIELDING [ppm] = 20.27 CHEMICAL SHIELDING FOR ATOM 2 ( H ) AVERAGE SHIELDING [ppm] = 28.38 STD DEV SHIELDING [ppm] = 1.53 : : : : : *** NSR CONSTANTS STATISTIC *** NSR CONSTANT FOR ATOM 1 ( F ) AVERAGE NSR XX-CONSTANT [kHz] = 3.80 STD DEV NSR XX-CONSTANT [kHz] = 3.63 AVERAGE NSR YY-CONSTANT [kHz] = 2.91 STD DEV NSR YY-CONSTANT [kHz] = 0.99 AVERAGE NSR ZZ-CONSTANT [kHz] = 3.15 STD DEV NSR ZZ-CONSTANT [kHz] = 1.34 NSR CONSTANT FOR ATOM 2 ( H ) AVERAGE NSR XX-CONSTANT [kHz] = -0.12 STD DEV NSR XX-CONSTANT [kHz] = 0.12 AVERAGE NSR YY-CONSTANT [kHz] = -0.06 STD DEV NSR YY-CONSTANT [kHz] = 0.01 AVERAGE NSR ZZ-CONSTANT [kHz] = -0.06 STD DEV NSR ZZ-CONSTANT [kHz] = 0.01 : : : : : :

the instantaneous NSR tensor diagonal elements and isotropic value along with its average are listed for the selected NMR atom in the SIMULATION keyword line. The NSR constant statistics at the end of the output are given for all atoms. Note also the NMR shielding statistics. Thus, NSR constants and NMR shieldings are always calculated together.