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Dear friend：
I see that VASP6 can calculate the electroacoustic coupling correlation, if given an optimized POSCAR, using the one-shot method, set the temperature T=0k, in principle should get the same POSCAR.T=0. file as the initial given POSCAR, only when the temperature is increased, such as 100K, 200K, 300K, it will be significantly different, but when I follow the steps to expand the cell, I do not get the consistent POSCAR.T= after running the one-shot0. This makes me a little incomprehensible. I'm also curious to see if this method is suitable for U-optimization.
Best wishes!
Quxiao

Dear Quxiao,

If I understood your question correctly, you would like to know why your POSCAR.T=0 is different from the initial POSCAR file. This is due to the fact that even at 0 K some phonons still exist, which can lead to a renormalization of the band gap (commonly referred to as zero-point renormalization). You can find more detail in
M. Engel, et al., Phys. Rev. B 106, 094316 (2022)

Dear Alexey:
Thank you very much for your previous reply. I have a new question. The system I encountered needs to consider strong correlations, so I added U related parameters. My system initially had spin, such as a total magnetic moment of 3, which I also set in my input file INCAR. I'm not sure if this is correct. I used a 2 * 2 supercell for calculation, with a total of 24 atoms. I will show you my INCAR, please help me explain. In addition, I tested KPOINTS with only one point Gamma and 15 * 15 * 1, and found that there are still significant differences. Is this normal? And for convergence purposes, should I test enough atomic numbers?
Best wishes！
Quxiao

Dear Quxiao,

I'm not sure I understood your question correctly. In your INCAR you set magnetic moment of 3 for each of 8 atoms, so the initial total magnetic moment in your system is 24. I don't know what system you are trying to model so it's hard to tell if it makes sense.
Also, this question is not related to your first question, so I would really appropriate if you could create a new topic for this new question and also please don't forget to attach the input and output files as described in the guidelines.