NUCIND
NUCIND = .TRUE. | .FALSE.
Default: NUCIND = .FALSE.
Description: Allows the nuclear-independent chemical shielding (NICS) to be calculated.
Warning: Not yet released!
This page contains information about a feature that will be available in a future release of VASP. In other words, currently you cannot use it even with the latest version of VASP. The information may change significantly until it is released.
In conjunction with LCHIMAG = True, NUCIND calculates the chemical shielding tensor [math]\displaystyle{ \sigma_{ij} }[/math] at positions off-nucleus, hence nuclear-independent chemical shielding (NICS) [1][2]. When NUCIND = True, by default these are calculated on the FFT grid NGX x NGY x NGZ in ppm. The output is written to NICS.
It is also written to vaspout.h5, if compiled with HDF5 support. You can find the data groups
/results/nics Group
/results/nics/grid Dataset {3}
/results/nics/structure Group
/results/nics/structure/position Group
/results/nics/structure/position/direct_coordinates Dataset {SCALAR}
/results/nics/structure/position/ion_sha256 Dataset {2}
/results/nics/structure/position/ion_types Dataset {2}
/results/nics/structure/position/lattice_vectors Dataset {3, 3}
/results/nics/structure/position/number_ion_types Dataset {2}
/results/nics/structure/position/position_ions Dataset {8, 3}
/results/nics/structure/position/scale Dataset {SCALAR}
/results/nics/structure/position/system Dataset {SCALAR}
/results/nics/values Dataset {9, 108, 108, 108}
and use py4vasp to access these, e.g., using
import py4vasp as pv
calc = pv.Calculation.from_path(".")
calc.nics.plot()
to select the isotropic chemical shielding [math]\displaystyle{ \sigma_{iso} }[/math] in 3D space. It will produce an isosurface of the shielding (positive) and deshielding (negative) over the crystal structure.
Alternatively, produce a 2D contour plot of the NICS in a plane:
import py4vasp as pv
calc = pv.Calculation.from_path(".")
calc.nics.to_contour(a=0.5)
It will result in a contour plot showing the isotropic chemical shielding [math]\displaystyle{ \sigma_{iso} }[/math] in the selected plane. The plane is selected as a fraction x of the lattice vector. Here, x=0.5 corresponds to half of the primary lattice vector [math]\displaystyle{ \mathbf{a} }[/math]. For the other lattice vectors use b=x or c=x.
For both the 2D and 3D plots, the isotropic chemical shielding is used by default. You can alternatively select the other properties (see LCHIMAG for details. Herzfeld-Berger convention is followed [3]) by inputting them as arguments into the functions, e.g., calc.nics.plot("anisotropic") or calc.nics.to_contour("span", a=0.5):
"isotropic"(default) - plot the isotropic chemical shielding [math]\displaystyle{ \sigma_{iso} }[/math]"anisotropic"- plot the anisotropic chemical shielding [math]\displaystyle{ \sigma_{ani} }[/math]"span"- plots the span [math]\displaystyle{ \Omega }[/math]"skew"- plot the skew [math]\displaystyle{ \kappa }[/math]
Alternatively, if the POSNICS file is present, then the positions defined within that file will be used. These chemical shielding tensors are printed in the OUTCAR file as follows:
nics 100
1.187143 -0.003408 -0.000000
-0.002977 -1.893648 -0.000000
-0.000000 -0.000000 -0.326272
Related tags and articles
LCHIMAG, NICS, LNICSALL, LPOSNICS, POSNICS
References
- ↑ P. von Ragué Schleyer, C. Maerker, A. Dransfeld, H. Jiao, and N. J. R. van Eikema Hommes, Nucleus-Independent Chemical Shifts: A Simple and Efficient Aromaticity Probe, J. Am. Chem. Soc. 118, 6317 (1996).
- ↑ Z. Chen, C. S. Wannere, C. Corminboeuf, R. Puchta, and P. von Ragué Schleyer, Nucleus-Independent Chemical Shifts (NICS) as an Aromaticity Criterion, Chem. Rev. 10, 105, 3842–3888 (2005).
- ↑ J. Mason, Conventions for the reporting of nuclear magnetic shielding (or shift) tensors suggested by participants in the NATO ARW on NMR shielding constants at the University of Maryland, College Park, July 1992, Solid State Nucl. Magn. Reson. 2, 285 (1993).