Electron Electron interactions in the fast-motion regime

[chris wedge]

I was wondering whether it is possible in Easyspin to include electron electron interactions and motional averaging. Garlic gives a clear message that it only works with a single S=1/2 so I intended to use chili even though my experimental data is possibly a little more towards the fast rather than slow-motional regime. After working out how to input the hyperfine interactions correctly I've got some simple code that will work with pepper, but chili gives an error:

Operands to the || and && operators must be convertible to logical scalar values.

From minimal example:

Code: Select all

Sys=struct('S',[1/2 1/2],'g',[2.0023; 2.0023],'Nucs','14N,14N',...
    'A',[20 20 80 0 0 0; 0 0 0 20 20 80],'lw',0.1,'logtcorr',-9,'ee',10)
Exp=struct('mwFreq',9.5)
chili(Sys,Exp)

I couldn't find anything in the documentation or forum saying Sys.ee can't be used with chili, but equally couldn't find examples in which they are used together. As you can probably guess the system in question is a dinitroxide; I'm getting some strange lineshapes in solution that I think are down to electron-electron interactions but I wanted to play with a simulated spin system to see if the line patterns can be reproduced. Is my best option simply to use pepper with isotropic A and g?

Thanks
Chris

[Stefan Stoll]

garlic is limited to a single electron spin, so using chili is the right approach. The theory underlying chili simulations is valid both in the slow-motional and the fast-motional regime.

The error message you get is a bug. We'll fix it and post a new version soon. Thanks for reporting!

[Stefan Stoll]

You can now download the new version 5.0.20, where this bug is fixed.

[patrick]

We are also dealing with a similar problem. But additionally to EE exchange and molecular motion for our case
of nitroxide biradicals there is a chemical exchange (conformational dynamics) and the simulation using chili function isn't sufficient,
therefore we would be thankful if you could give us a advice or access to source code of the function.

[Stefan Stoll]

EasySpin currently does not support chemical exchange, but I just uploaded a function that implements it to the file exchange forum. Download it from there - hopefully it's useful.

[chris wedge]

Thanks for the bug fix.
Am I correct in thinking that while chili accounts for motion as far as the modulation of hyperfine and g anisotropy is concerned, it would not allow for modulation of the electron-electron coupling i.e. the tumbling is treated correctly in the case of a rigid biradical but would be inappropriate for a flexible biradical in which the electron-electron interaction is being averaged over a range of values?
I assume being a rather specific problem there is no way in built in to easyspin to also include the modulation of the size of the electron-electron coupling, so as to get the classic alternating linewidth pattern that my synthetic colleagues would like to see perfectly reproduced...
Thanks

[Stefan Stoll]

chili can only model rotational diffusion. Apart from that, all spin Hamiltonian parameters are fixed. Unfortunately, EasySpin doesn't currently implement any other modulation effects.

For modeling the modulation of the electron-electron coupling, have a look at the function for chemical exchange posted in the file exchange forum.