Simulation with rotational barrier

[lorenz]

Hi,

I want to simulate a EPR spectra with chili. I expect two nuclei with highly rhombic HFS tensors. But they can do a hindered rotation due to a rotational barrier.
Is it possible to manage this problem with chili?
I think there is currently a hindered rotation implemented only for one nucleus with a ordering potential. Is this right?
Is there any other way to simulate this problem with easyspin?

Kind regards
Lorenz

[Stefan Stoll]

Assuming the two nuclei are both rotating around the same dihedral angle, you just have to make sure their relative hyperfine tensor orientations are entered. Then, you can model the hindered rotation with ordering potentials in chili. Otherwise, if the two nuclei are independent, it is not possible to do with chili.

[lorenz]

Thanks for your answer. I have explained something wrong.
I have two rhombic HFS tensors rotating around the same dihedral angle. But there is thrid nucleus (quit isotropic HFS) which is not rotating.
When I run chili with all three nuclei, it does not work.
Is there a way to simulate this system with chili?
Or is it possible to simulate the spectra with the 2 ansiotropic nuclei and convolute it afterwards with the isotropic nucleus spectra?
Is there a way to do this with easyspin?
All HFS-couplings are of the same magnitude. (Between 60MHz and 100 MHz)

[Stefan Stoll]

In chili, it is not possible to apply different correlation times to different nuclei, since chili is designed to model rotational tumbling. What you are looking at is more like a chemical exchange situation. However, if your third nucleus indeed has isotropic HFC, then you might get away with chili. You can use Opt.PostConvNucs = 3 to invoke the post-convolution. Alternatively, you can run the full SLE algorithm with all three nuclei using Opt.LiouvMethod = 'general'. This will be quite slow though. Lastly, check out the EasySpin file exchange for a program that can handle chemical exchange.

[lorenz]

sorry but both ways don't work.
Maybe I've done something wrong:

1. Simulate with full SLE:

%Define Spin-System
Sys.S=1/2;
Sys.g=2.0023;
Sys.Nucs='1H,1H,1H';
Sys.lwpp=[0.2 0.2];
Sys.A=[-98 -62 -21;-97 -61 -20;102 102 102];
Sys.AFrame=[2 30 102;-15 30 -62;0 0 0]*pi/180;
Sys.logtcorr=-9;
Sys.lambda=2;

%Define Experiment
Exp.mwFreq=9.5;
Exp.nPoints=1024;
Exp.Range=[330 350];

%Define Options
Opt.LiouvMethod = 'general';

chili(Sys,Exp,Opt);

Matlab error:
Error using chili (line 451)
Ordering potential not supported for Opt.LiouvMethod='general'.
Error in chili (line 109)


2. PostConvolution does not wotk even by removing the ordering potential:

%Define Spin-System
Sys.S=1/2;
Sys.g=2.0023;
Sys.Nucs='1H,1H,1H';
Sys.lwpp=[0.2 0.2];
Sys.A=[-98 -62 -21;-97 -61 -20;102 102 102];
Sys.AFrame=[2 30 102;-15 30 -62;0 0 0]*pi/180;
Sys.logtcorr=-8;


%Define Experiment
Exp.mwFreq=9.5;
Exp.nPoints=1024;
Exp.Range=[330 350];


%Define Options
Opt.PostConvNucs =[1 2];

chili(Sys,Exp,Opt);


matbal error:
Attempt to reference field of non-structure array.
Error in chili (line 483)
Error in chili (line 109)

[Stefan Stoll]

1. Yes, I realize now that this is unfortunately not yet implemented.

2. This is a bug. We will need to fix it. Thanks for reporting! For now, you can work around it by not using Sys.lwpp and by using convspec instead to convolute the spectrum with a lineshape.

[lorenz]

Hi,
Opt.PostConvNucs works by removing the linewidth. But I receive the same error massage by applying Sys.lambda.:
Error using chili (line 451)
Ordering potential not supported for Opt.LiouvMethod='general'.

[Stefan Stoll]

Opt.LiouvMethod='general' can currently not handle ordering potentials.

[lorenz]

Ok.
Thank you.