Python Materials Genomics (pymatgen) is a robust materials analysis code that defines classes for structures and molecules with support for many electronic structure codes. It powers the Materials Project.
I've just been going through the NMR analysis module and noticed the comment about the sign inconsistency across the two papers referenced. I'm not sure there is a sign inconsistency between the papers, and the sign chosen in the code appears to be incorrect (I may be wrong, so double-check!)
In equation 20 from Magn. Resonance Chem. 2008, 46, 582-598 they give the sign as $\sigma{iso}$ - $\sigma{22}$ and in Solid State Nucl. Magn. Resonance 1993, 2, 285-288 they give the same way round for shieldings. However, if talking about shifts ($\delta$) instead of shieldings ($\sigma$) then the sign should be reversed (i.e. $\delta{22}$ - $\delta{iso}$) as it is in the last line of skew definition in the 1993 paper.
In general there might be other places where NMR conventions are given in terms of the experimentally measured chemical shifts but VASP/CASTEP etc deal only in absolute magnetic shieldings so the conventions should sometimes be reversed.
I've just been going through the NMR analysis module and noticed the comment about the sign inconsistency across the two papers referenced. I'm not sure there is a sign inconsistency between the papers, and the sign chosen in the code appears to be incorrect (I may be wrong, so double-check!)
In equation 20 from Magn. Resonance Chem. 2008, 46, 582-598 they give the sign as $\sigma{iso}$ - $\sigma{22}$ and in Solid State Nucl. Magn. Resonance 1993, 2, 285-288 they give the same way round for shieldings. However, if talking about shifts ($\delta$) instead of shieldings ($\sigma$) then the sign should be reversed (i.e. $\delta{22}$ - $\delta{iso}$) as it is in the last line of skew definition in the 1993 paper.
https://github.com/materialsproject/pymatgen/blob/720fdf86539236c737f12250ae71d68e3872c616/src/pymatgen/analysis/nmr.py#L113
In general there might be other places where NMR conventions are given in terms of the experimentally measured chemical shifts but VASP/CASTEP etc deal only in absolute magnetic shieldings so the conventions should sometimes be reversed.