Wrong sign in NMR convention?

[jkshenton]

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.

pymatgen/src/pymatgen/analysis/nmr.py

Line 113 in 720fdf8

# There is a typo in equation 20 from Magn. Resonance Chem. 2008, 46, 582-598, the sign is wrong.

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.

[JaGeo]

Thank you for reporting this. I am personally not an expert for this module.

@shyuep, do you by chance have some insights here? This comment has been added more than 8 years ago.