low field Mn(II) spectra in pepper

[Joseph]

I am using pepper to simulate the spectrum of an Mn(II) impurity in calcium carbonate. I can do a good job at 9.5 GHz but can not come close at low fields (300 MHz). I suspect it is looping transitions. Is there any way to eliminate or minimize this problem?

[Stefan Stoll]

If you have looping transitions, first make sure that you use matrix diagonalization and not perturbation theory (see Opt.Method. Also, for a powder simulation with looping transitions you might need to substantially increase the number of orientations (see Opt.nKnots).