EasySpin forum

Posted: **Tue Jan 29, 2019 3:53 am**

I have found that simulation of the spectrum of biradicals by pepper function gives wrong results with Opt.Method='hybrid' parameter. The spectra always looks as ones with J>>A regardless Sys.J parameter. Here the script illustrating the problem.

Code: Select all

clear, clf
aN=28;
J=aN*[0.01 0.3 0.5 0.9 1.5 2 2.5 3.5 5 7 9 12 20 40 1000];
Exp.mwFreq =9.66;
Exp.Range = [338 350];
Sys.S = [1/2 1/2];
Sys.Nucs='14N,14N';
Sys.A=mt2mhz([aN 0.0;0.0 aN;]/10);
Sys.g = [2.0060; 2.0060];
Sys.lw = [0 0.15];
Exp.nPoints=4096;
Opt.Method='hybrid';
for i=1:numel(J)
Sys.J=J(i);
FitOpt.Method = 'simplex fcn';
FitOpt.Scaling = 'maxabs';
[x,y1(i,:)]=pepper(Sys,Exp,Opt);
end
stackplot(x,y1,1,1);

Is it a bug or restriction of hybrid method?

Posted: **Wed Jan 30, 2019 3:29 am**

Not sure if this is a bug. The documentation says:
" 'hybrid' indicates matrix diagonalization for all the electron spins, and perturbation treatment for all nuclei"

In the case of exchange coupling, the first step, i.e. the diagonalization for the electron spins, will always lead to a singlet-triplet basis in the absence of hyperfine interaction (and identical g-values).

Posted: **Wed Jan 30, 2019 10:28 am**

nwili is right. Here is a brief demonstration script:

Code: Select all

clear, clc

Sys.S = [1/2 1/2];
Sys.J = 0.01;
H = sham(Sys,[0 0 350]);

[V,E] = eig(H)

V shows complete mixing of the |alpha,beta> and the |beta,alpha> states, no matter how small J is.

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Simulation of biradicals in hybrid mode

Simulation of biradicals in hybrid mode

Re: Simulation of biradicals in hybrid mode

Re: Simulation of biradicals in hybrid mode