Formalisms and approximations

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Joined: Tue May 24, 2022 6:32 am

Formalisms and approximations

Post by NMR-trainee »

Hello prof. Kuprov.

As I'm testing my codes for spin polarization graphs, I noticed strange differences between formalisms and 'nmr' and 'labframe' assumptions.

First of all, am I right in thinking that different formalisms should give the same output, given that the code can be run with both formalisms?

Second, should the 'nmr' assumption give different results in low field spin polarization, than the 'labframe' assumption?

I want my code to have no approximations, so I figured 'labframe' would be the best choice, with 'sphten-liuov' formalism. But that produces unphysical results in my case, when the magnetic field is at 6.5mT. If I change only the formalism to 'zeeman-hilb', it gives correct results. And with 'zeeman-hilb', the 'nmr' and 'labframe' assumptions give the same result, whatever the magnetic field might be. But in 'sphten-liuov', the 'nmr' assumption gives correct results, even at 6.5mT field.

So the problem is, that I do not know when my code is doing approximations and when it isn't. And what formalism I should use to always get physical results with no approximations.

I attached said code as a picture. Thanks for the help!
Codespinpol.PNG (268.63 KiB) Viewed 179 times
Posts: 106
Joined: Mon Mar 29, 2021 4:26 pm

Re: Formalisms and approximations

Post by kuprov »

Different formalisms (zeeman-liouv, sphten-liouv) would of course produce the same answer, but different assumptions would not.

Assumptions refer to "what Spinach can assume it can ignore or approximate". For example in high-field NMR, weak coupling is a common assumption. It would of course be erroneous in low-field NMR.

Labframe is essentially the only possible choice in low-field magnetic resonance. Indeed, it corresponds to no approximations of any kind.
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