Electronic minimization issues with MoTe2 in the presence of electric field.

[santanumahapatra]

Thank you for your response. I have one more question. When I run the VASP calculation for NSW=0 in the presence of electric field, I get very high energy value with the below INCAR:

Code: Select all

PREC=Accurate
EDIFF=1e-5
EDIFFG=-1e-2
ISTART=0
ENCUT=600.0
NSW=0
ISIF=2
IBRION=2
POTIM=0.02
ISMEAR=1
SIGMA=0.05
LDIPOL = .TRUE.
IDIPOL = 3   # for Z direction
EFIELD = 0.1   # eV/A**
DIPOL = 0.0 0.0 0.5 
#DIPOL = 0.4273  0.3434  0.4888
#LNEBCELL = .TRUE
#EFIELD_PEAD=0.0 0.0 0.5

But if I only use the PEAD tag and setting off the other Efield tags, the energy I get for single step calculation is the same as that in the absence of Efield.
Does this mean that I should not use NSW=0 when I am using the EFIELD tags and instead do a full relaxation of the structure? I am a bit confused here.

I have tested with different DIPOL values and I get different values of high energy. I believe this has something to do with the proper setting of DIPOL, howver, I am not very sure about how to calculate it accurately.

Below is the test POSCAR:

Code: Select all

EA0     4.078  5.542 18.703 95.19 88.97 91.64 Sym.group:    0
1.0
    4.077563     0.000000     0.073334
   -0.149723     5.517480    -0.501556
    0.000000     0.000000    18.703023
  Mo  Te
   2   4
Direct
    0.486712     0.643803     0.988911 
    0.000000     0.000000     0.000000 
    0.003467     0.661042     0.886774 
    0.971906     0.500467     0.081632 
    0.522218     0.154394     0.909593 
    0.483926     0.984842     0.100588 

Kindly suggest

[alexey.tal]

Dear santanumahapatra,

I have moved your post to a separate topic as this question is unrelated to NEB, so I think it deserves its own topic.

I think that the first issue you need to resolve is the structure, which doesn't seem to me to be correctly set.
Here is what your POSCAR structure looks like:

pic.png

I would not expect any meaningful results from comparing the calculation with or without the field if the atomic structure is not set correctly, i.e, if it doesn't correspond to a (meta)stable state.

Best wishes,
Alexey

[ahampel]

Dear santanumahapatra,

just a small addition to what Alexey said: please remember to move the position marked by the DIPOL flag to where your layer (maximum of charge density is located), i.e. in this case it would be more reasonable to set DIPOL= 0.0 0.0 0.0 . This should affect the calculation quite a lot.

Note, that I closed our old discussion about this: https://vasp.at/forum/viewtopic.php?t=1 ... =15#p30391 for now.

[santanumahapatra]

Thank you for your response.
I really understand that the position of DIPOL plays a crucial role in what I am trying to simulate. Can you provide any tutorial about how to place the co-ordinates of DIPOL accurately or any tool which directly finds the right position for DIPOL for a particular POSCAR? I have read VASP documentation on this but could not understand how it changes for different lattice co-ordinates. Is it just the midpoint of the z-axis or is there any complex calculation involved?

Regards.

[alexey.tal]

As described on our wiki, for calculations of isolated molecules and surfaces with the dipole correction, use DIPOL as the center of mass of the atoms in your cell. Additionally, note that for surfaces, only the component normal to the surface is meaningful.

[santanumahapatra]

Thank you for your answer.
If DIPOL is the COM, then based on the POSCAR mentioned above, if I take the mass of Mo and Te as 95 and 127 amu resp, the COM comes as (1.6634,2.7917,9.0279) in Cartesian co-ordinates. Is it the same as writing 0 0 0 for DIPOL as you mentioned?
Sorry if I didn't understand any key point.
Thanks in advance for your clarification.

Regards

[ahampel]

I am a bit confused. I looked at your most recently POSCAR:

POSCAR.jpg

And there is nothing at z=0.5 (z=9.03 a) or am I mistaken? So I would still place the coordinates provided to DIPOL where the atoms are in the layered material. Since you calculate the dipole correction around the c axis I would specify it at 0.0 0.0 0.0 . Does this sounds reasonable?

Best,
Alex

[santanumahapatra]

Thank you, I think I got it.
One more question, if I want to apply a negative electric field instead of a positive one, do I only need to change the sign of EFIELD? Is there any other change required?
Regards,