About LDAUL

[pooja_rani]

Hello,

I am trying to perform phonon calculations using the PHONOPY method for
FePS₃. In this, 2 Fe atoms have up spin and 2 have down spin. So now I
define LDAUL = 2*2 (for d-orbital and 2 for the two types of Fe, spin up
and down) according to "Default: LDAUL = NTYP*2," and then I am getting
results, but I am not sure if this is the right way to define it because
using this I am not getting any negative frequencies. But if I set LDAUL=2
only, then I am getting negative frequencies. Please suggest which is the
right way.

Warm Regards,
Pooja Rani

[alexey.tal]

Dear Pooja Rani,

Thank you for your question.

LDAUL should be set for every species and -1 should be set for species where no U is applied. From your description it seem to me that you only set U for Fe atoms. Without seeing all the files I cannot to tell if the way you set your calculation is correct. Could you please provide all the input and output files as described in the forum guidelines?

Best wishes,
Alexey

[pooja_rani]

Dear Alexey,

Thank you so much for the reply!
Here, I am attaching the INCAR and POSCAR files that I am using. Please have a look and suggest. I am trying this way of using LDAUL=4; maybe it could be wrong. But by using this, I am not getting any negative frequency.

Warm Regards,
Pooja Rani

[alexey.tal]

You should set LDAUL=2 (l-quantum number) if you want to apply the on-site interaction to the d-electrons. The negative frequencies usually indicate that your system is not stable. Have you relaxed your system with the provided value U?