Difference between "symmetries of the Bravais lattice" and "symmetries of the crystal with FFT grid" in kgrid.x

[Kostas Fykouras]

Dear experts,

I have question about the difference between "symmetries of the Bravais lattice" and "symmetries of the crystal with FFT grid"  that the file kgrid.log produces.

It seems that If I look at the Bravais lattice symmetries my system is P4/mmm while the FFT symetries say that my system belongs on the triclinic P1 group.

So

1) How can I 'read' the space group of my lattice from the kgrid.log file. Should I look at the bravai lattice symmetries or the FFT symmetries?

2) Why is there such a big difference between them?

Thanks in advance to anyone who takes time to read this post.

All the best,

Kostas

[Zhenglu Li]

Dear Kostas,

In standard DFT calculations, the DFT will first find the symmetry of crystal (Bravais lattice), and then make a decision on the FFT grid that is compatible with crystal symmetry.  In kgrid.inp, you can find the FFT grid from DFT output and put it there.  Sometimes inconsistencies still remain depending on the algorithm of DFT codes.

In general, one should only use crystal symmetry to reduce kgrid.  To make it simple, one can just set FFT grid as 0 0 0 in kgrid.inp.

Best,

Zhenglu

---

From: Kostas Fykouras <kostasf...@gmail.com>
Sent: Friday, December 13, 2024 2:23 AM
To: BerkeleyGW Help <he...@berkeleygw.org>
Subject: Difference between "symmetries of the Bravais lattice" and "symmetries of the crystal with FFT grid" in kgrid.x

 

Dear experts, I have question about the difference between "symmetries of the Bravais lattice" and "symmetries of the crystal with FFT grid"  that the file kgrid. log produces. It seems that If I look at the Bravais lattice symmetries my system

--
You received this message because you are subscribed to the Google Groups "BerkeleyGW Help" group.
To unsubscribe from this group and stop receiving emails from it, send an email to help+uns...@berkeleygw.org.
To view this discussion visit https://groups.google.com/a/berkeleygw.org/d/msgid/help/ad6b99d4-b4f3-4c9c-9ba1-5dbc0290c0f4n%40berkeleygw.org.