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Posted: **Wed Apr 01, 2015 4:38 pm**

Hi,

I'm trying to simulate nitroxide biradical spectrum. Looking at the example "Two coupled electrons", I understand how to specify g-tensors:

Sys.S = [1/2 1/2];
Sys.g = [2 2.05 2.1; 2.2 2.25 2.3]; <--- g-tensors are stacked as new matrix lines

However, adding following for A-tensor would not work:

Sys.Nucs = '14N, 14N';
Sys.n= [1 1];

Sys.A=[20 20 100; 20 20 100]; <--- this is inconsistent with the number of specified nuclei and produces an error. 2x6 matrix is apparently expected?!

Can you please explain the logic of correct A-tensor definition? Thanks!

Posted: **Thu Apr 02, 2015 6:33 am**

How you have it written right now each spin is coupled to two nitrogens. When dealing with multiple electron spins what you define for the nuclear couplings is applied to both the electrons. So for the hyperfine matrix A, if both electron spins are interacting with a single nitrogen then you would have a 1x6 matrix, where the first three values correspond to the hyperfine interaction with the first spin and the next three with the second spin.
If both electron spins are interacting with two nuclei then you'd have a 2x6 matrix and so on. If only one of the electrons has an interaction with a nuclei and not the other then you'd place zeros for the three values.

So something like this:

Code: Select all

Sys.S = [1/2 1/2];
Sys.g = [2 2.05 2.1; 2.2 2.25 2.3];
Sys.ee = 1;
Sys.Nucs = '14N';
Sys.n= 1;
Sys.lwpp = 0.1;
Sys.A=[20 20 100 20 20 100];

Exp.mwFreq = 9.5;

pepper(Sys,Exp);

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