Ax and Ay "interchanging" in calulation

[iis042]

Hi,


I don't know if this is actually an easpspin question, but I hope someone might be able to help with it.
I am having some problems in understanding my results after calculating EPR parameters with B3LYP and PBE0 in orca and analyzing them using easyspin and I hope someone can help me understanding this.

As I said I have calculated EPR parameters using B3LYP and PBE0, the inputfiles are given as attachments for step 60 and 72. In step 60 the values fro B3LYP and PBE0 are approximately the same, but at step 72 Ax and Ay has switched. Both methods have the same geometry-files as start, also attachment. I am doing the calculations for different geometries, scanning the dihedral angle in a histidine brace with copper and when I try to plot the EPR parameters I see that the two methods give different results. For PBE0 it seams that the Ax and Ay values between step 70 and 80 are interchanged compared to the results from B3LYP, see the attached figure.

So I am hoping someone can help me understand what is happening here?
I was thinking it probably had to do with the different methods, but I don’t understand how or what in the methods that gives this difference?

Thanks in advance for the help.

Best, Ingvild

[Stefan Stoll]

Just looking at the principal value of the A tensors is not enough, you also need to look at the orientations (Euler angles, AFrame in EasySpin). It could be that ORCA is changing the frame definition from one step to the other. That would then just mean that the 'x' and 'y' names have changed, but the actual directions in space for the principal values haven't much.