Monday, 25 January 2021

Chemical shielding tensors

How do you visualise a tensor field? A 3x3 tensor as a function of the 3 spatial coordinates makes a 12-dimensonal object. How do we visualise a 12-dimensional object using a 2-dimensional screen? This is the problem we encountered trying to visualise the chemical shielding tensor, which is a common aromaticity criterion. The solution: we compute the principal axes of the tensor and represent those using little dumb-bells at different points in space providing us at least a coarse-grained description.

 To get the full story, check out our preprint “3D Visualisation of chemical shielding tensors to elucidate aromaticity and antiaromaticity” available on ChemRxiv or this blog post.

Here, I just wanted to show a few more computer graphics. This, for example, are the in-plane shielding tensors shown with our new VIST method in connection with the ACID isosurface as computed via GIMIC.

For comparison, the NICS(1) tensors along with the magnetically induced current densities also computed using GIMIC. Diatropic currents, giving rise to positive shielding are shown in blue; paratropic currents in red. Diatropic currents dominate, hence we see positive (blue) shielding.

The code will be released through TheoDORE once I have the time to make it reasonbly well documented and user friendly.

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