The same Stev operator, different assignment forms, different simulation results in easyspin-6.0.0-dev.29

[YanQing]

code 1:

clear, clf; clc;

Exp.mwFreq = 9.8;
Exp.Range = [200 500];
Exp.nPoints = 1e5;

Opt.Verbosity = 2;
Opt.nKnots = 30;

Sys.S = 5/2;
Sys.g = [2 2.003];
Sys.Nucs = 'Mn';

Sys.A = 550;

Sys.B20 = -29;
Sys.B21 = -232;
Sys.B22 = -191;
Sys.B40 = 1.56;
Sys.B41= -6.3;
Sys.B42 = 9.7 ;
Sys.B43 = -40;
Sys.B44 = 10.3;

Sys.lw = [0.3 0.2];

[b,spc,trans] = pepper(Sys,Exp,Opt);

plot(b,spc,'linewidth',1.5);
set(gca,'LineWidth',1,'FontSize',15);
xlabel('Magnetic field (mT)');
grid on;
axis tight;

%.................................................................

code 2:

clear, clf; clc;

Exp.mwFreq = 9.8;
Exp.Range = [200 500];
Exp.nPoints = 1e5;

Opt.Verbosity = 2;
Opt.nKnots = 30;

Sys.S = 5/2;
Sys.g = [2 2.003];
Sys.Nucs = 'Mn';
Sys.A = 550;
Sys.B2 = [-191 -232 -29 0 0];
Sys.B4 = [10.3 -40 9.7 -6.3 1.56 0 0 0 0];
Sys.lw = [0.3 0.2];

[b,spc,trans] = pepper(Sys,Exp,Opt);

plot(b,spc,'linewidth',1.5);
set(gca,'LineWidth',1,'FontSize',15);
xlabel('Magnetic field (mT)');
grid on;
axis tight;

[Stefan Stoll]

In your first system, the field B21 etc are not recognized by EasySpin, so the spectrum gets simulated without any higher-order operators in the Hamiltonian. In your second system, the fields B2 etc are recognized, so the high-order terms are included.

[YanQing]

Thanks;

I found that this Stev operator seems to have different descriptions in different versions. There are several versions that do not support some old assignment formats. For example, the new version does not seem to support aF items anymore. Should we use the format in the developer version? Will this difference be unified in the new version?

[Stefan Stoll]

The input syntax for v6.0 (which is still under development) will not be backwards compatible with the one from v5.2.

For now, I suggest to stick with v5.2 if you want a stable version.

Alternatively, use the v6.0 development version, which has many improvements. For example, in v6.0 you can rotate Stevens operator terms using Sys.B2Frame. The v6.0-dev version is as well tested as v5.2, if not better. However, the downside of using v6.0-dev is that some details of the interface might still change until the final v6.0.