Hello experts, I have been trying to optimize a 2D structure with 3 atoms in the unit cell. I am using CG by varying the cell dimensions. I have optimized the k-points and mesh cutoff. But no matter how many times I try to relax the structure, it is giving a negative phonon frequency at the gamma point. The structure is experimentally achieved structure with available .cif file. The cell dimensions achieved after relaxation are the same as the experimentally achieved one, with less than 2% deviation, and theoretical work publications show that the structure should come out to a stable one with no negative frequencies.
Where can be the issue? I am using fully relativistic .psf files and spin-polarization is on. Can basis set optimization be an issue? Help please. Regards, Sunetra Das.
