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materialsproject / pymatgen

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.
https://pymatgen.org
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Wrong sign in NMR convention? #3959

Open jkshenton opened 2 months ago

jkshenton commented 2 months ago

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.

JaGeo commented 2 months ago

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.