I am trying to calculate the phonon dispersion curve for a 2D material. Once I have properly optimized the primitive structure until forces are completely negligible, I created a supercell. However, when I computed the forces for this undistorted supercell, there were huge forces.
One of the things I have tried is increasing the grid NGX,Y,Z manually in the input. But, when I check the OUTPUT it seems that VASP is overriding the grid I have selected. Below follows the relevant parts of my output:
max r-space proj IRMAX = 1 max aug-charges IRDMAX= 423666
dimension x,y,z NGX = 180 NGY = 180 NGZ = 200
dimension x,y,z NGXF= 360 NGYF= 360 NGZF= 400
support grid NGXF= 720 NGYF= 720 NGZF= 800
(...)
I would recommend the setting:
dimension x,y,z NGX = 129 NGY = 129 NGZ = 175
(...)
NNGXGis ok and might be reduce to 130
NGY is ok and might be reduce to 130
NGZ is ok and might be reduce to 174
Broyden mixing: mesh for mixing (old mesh)
NGX = 65 NGY = 65 NGZ = 87
(NGX =360 NGY =360 NGZ =400)
gives a total of 367575 points
It seems that VASP is not using the grid I define in the input.
I wonder how to force to get the grid I want and solve the problem with the forces in the supercell cell
FORCES and GRID in Supercells
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Re: FORCES and GRID in Supercells
Check if there is no mistake in producing the supercell.
For primitive cell and the supercell you should get
similar forces (k-point sampling should be proportionally
decreased).
For primitive cell and the supercell you should get
similar forces (k-point sampling should be proportionally
decreased).