Hello Everyone,
I am confused with the phonon dispersion I got for the material under study.
Near to 0 cm-1 all the phonon bands are positive but we are getting a negative band appearing near -500 cm-1.
Is this referring to numerical noise or should this relate to instability of the structure.
I already relaxed the structure and checked the pressure corresponding to 0 GPa.
Ecut used : 70 Ry
Ecutrho : default value (4* ecut)
k points : 8 8 8 for Scf calculations
ngridq: 4 4 4 and also tried with 8 8 8
The file is attached below, kindly share your reviews.
Thanks,
Abhinav Nag
Can you visualize the mode with -500 cm-1?
1: If you can figure out the direction of wave vector corresponding to this mode, you can displace atom/atoms along the direction of the wave vector (say ~0.1-0.2 Ang) and relax the structure again.
2: You may want to break the symmetry by displacing atoms randomly and relax again.
This is a normal double sided spectrum. The single sided spectrum appears in the RHS half of your Brillouon zone.
The negative frequencies just mean that the material (in the considered structure) is unstable under conditions set. At least in temperature You set (dft usually is performed at T=0). see e.g. https://doi.org/10.1103/PhysRevResearch.2.033108 Sometimes it can be caused by not properly optimalized structure taken to phonon calculations.
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