M_INT versus MW_INT in constrained magnetic calculations

[sophie_weber]

Hello,
I wanted to check something about constrained magnetic calculations using I_CONSTR_M=1 (constraining direction, not magnitude). I know that in the OSZICAR file, two values are printed related to magnetic moments, one being the M_INT, or the magnetization density integrated over RWIGS, and MW_INT which is the so-called "smoothed integrated moment" which is the value that actually enters the penalty energy. I know from the example on the VASP wiki that it is normal and expected for the magnitudes of these values to be slightly different, however, looking at my calculations recently, I noticed that my MW_INT is really quite a bit smaller than my non-smoothed, M_int (like 1.6 uB versus 2.6 muB). I never really worried about this because in my calculations I was able to get the moments to point exactly in the direction I wanted them, my penalty energies were really tiny, the total energies do what I expected as I change the direction of the moments, and the calculations are extremely reproducible across different VASP versions and architectures. But I thought I should check whether indeed, such a difference in the values of M_int and MW_int is not problematic provided that the value of MW_int is "large enough", and moreover, how I can tell what "large enough" constitutes.

I attached example input files and relevant outputs for reference.
Thanks very much in advance!
Best
Sophie

[fabien_tran1]

Hi,

In order to comment on your observations, one would need some experience with the method. Therefore, I moved your post to "From Users for Users" to make it more visible to other VASP users. Also, if not already done, you may look at this paper https://doi.org/10.1103/PhysRevB.91.054420.

[sophie_weber]

Alright, thanks a lot! I look forward to responses. And thanks for the paper, I have read this before and indeed, it does seem like if you vary RWIGS you should be able to in principle get your smoothed integration density to approach the true magnetic moment...I'm just wondering whether the results can still be reliable when this is not the case.