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Posted: **Fri Aug 13, 2021 12:25 am**

Hello,

I would like to calculate the effect of electric field on the migration energy barrier of a molecule on a symmetric slab using NEB calculations (e.g., VTST). I intend to use IDIPOL for energy corrections and would also like to use LDIPOL for potential and force corrections. However, the unit cell I need to construct the slab is monoclinic, with a non-orthogonal angle in the direction perpendicular to the surface.

1. I was wondering about the limitation of LDIPOL corrections in this case, and since NEB simulations rely on forces, would it be an issue?
2. Can the calculation of adsorption energy as function of electric field intensity be affected? As the relaxed geometry at each electric field intensity also depend on force minimization.
3. What type of system the restrictions of LDIPOL apply to? Asymmetric slabs and/or cubic charged unit cell only?

Thank you for any information you can provide.

Best,
Michel.
PS: I am using VASP 5.4.4.

Posted: **Wed Aug 18, 2021 4:10 am**

Hi Michel,

Interesting project! This specific case has not been tested, so it is difficult to make a definite statement.

About the construction of your slab. Is one lattice vector perpendicular to the surface? This can always be achieved. Consider for instance hexagonal Ti. You can construct slabs, e.g., using pymatgen in the following way:

Code: Select all

from pymatgen.core import Structure
from pymatgen.core.surface import SlabGenerator

# read structure
mystruc = Structure.from_file( "Ti_mp-72_computed.cif" )

# generate slab
slabgen = SlabGenerator(mystruc, (1,1,1), 10, 10)
slab   = slabgen.get_slabs()[0] 
slab2 = slab.get_orthogonal_c_slab()

# write POSCAR 
slab.to( fmt="poscar", filename="POSCAR.slab" )
slab2.to( fmt="poscar", filename="POSCAR.orthogonal_c_slab" )

The resulting POSCAR files are attached.

For more details, I need to understand the symmetry of your calculation. To this end, please upload the input files. Particularly, the POSCAR file. Alternatively, you can read the documentation on monopole, dipole, and quadrupole corrections on the VASP Wiki.

Best regards,
Marie-Therese

Posted: **Wed Aug 18, 2021 5:01 am**

Hi Marie-Therese,

Thank you very much for your reply. Indeed, I could find a way to have the direction perpendicular to the slab surface orthogonal to the other two directions. So I should be able to avoid the restrictions of using LDIPOL as stated in the VASP wiki

.

Best wishes,
Michel.

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