Simulating two interacting S=1/2 systems

[Karim]

I am trying to simulate the cw-EPR spectra of 2[4Fe-4S] cluster ferredoxin. The protein has two interacting S =1/2 iron sulfur clusters. The exp g values for the EPR spectra are 1.83, 1.89, 1.95, 2.01, 2.05 and 2.11. I am using the following script:

Sys1.S = 1/2;
Sys2.S = 1/2;
Sys1.g = [2.01 2.05 2.11];
Sys2.g = [1.83 1.89 1.95];
Sys1.lw = 3;
Sys2.lw = 3;
Vary1.lw = .5;
Vary2.lw = .5;
Vary1.g = [.05 0.05 .05];
Vary2.g = [.05 0.05 .05];
Exp.mwFreq = 9.7;
Exp.Range = [300 390]
Exp.Temperature = 15;
Exp.ModAmp = 1;
esfit('pepper',spc,{Sys1, Sys2},{Vary1, Vary2},Exp);

The simulated spectra does not fit the exp data very well. I wanted to know if I the script lacks any critical piece of information. Any input would be helpful.

Thanks
Karim

[Stefan Stoll]

If the two clusters are coupled, you need to include both of them in the same spin system structure and add a coupling in Sys.ee. See the documentation on spin systems, which contains a section on electron-electron couplings.