Voltage-Current characteristics - Electric field

Question on input files/tags, interpreting output, etc.

Please check whether the answer to your question is given in the VASP online manual or has been discussed in this forum previously!

Moderators: Global Moderator, Moderator

Post Reply
Message
Author
karthik_hj
Newbie
Newbie
Posts: 23
Joined: Wed Jul 20, 2022 2:24 pm

Voltage-Current characteristics - Electric field

#1 Post by karthik_hj » Thu Jul 28, 2022 6:54 am

I want to simulate the effect of a voltage of 3V on a 2D structure.

Would it be right if I give it in VASP with the help of an electric field?

And if so, what is the equivalent of 3V in terms of electric force as VASP gives it in units of eV/Å which is a force.

OR is there any other way to simulate the effect of a voltage in VASP

henrique_miranda
Global Moderator
Global Moderator
Posts: 414
Joined: Mon Nov 04, 2019 12:41 pm
Contact:

Re: Voltage-Current characteristics - Electric field

#2 Post by henrique_miranda » Thu Jul 28, 2022 4:12 pm

You can use the EFIELD tag which is specified in units of eV/Å.
You have to set it depending on the length of the cell in the direction in which you apply the field.

karthik_hj
Newbie
Newbie
Posts: 23
Joined: Wed Jul 20, 2022 2:24 pm

Re: Voltage-Current characteristics - Electric field

#3 Post by karthik_hj » Fri Jul 29, 2022 4:28 am

Yeah EFIELD tags are fine.

But how to find the equivalent for 3V in terms of eV/Å ?

I am planning to give along the lattice parameter 'c' . My 'a' 'b' 'c' are 3.34 3.34 and 12.25 respectively

henrique_miranda
Global Moderator
Global Moderator
Posts: 414
Joined: Mon Nov 04, 2019 12:41 pm
Contact:

Re: Voltage-Current characteristics - Electric field

#4 Post by henrique_miranda » Fri Jul 29, 2022 1:31 pm

E -> Energy
V -> Potential (Energy as well)
q -> Electron charge
Ef -> Electric Field
F -> Force
d -> length

Consider the following relations
E = F*d (2)
E = q*V (3)

The potential difference V across the length d when an electric field Ef is applied is given by:
q*V = F*d -------- E=E using (3) and (2)
q*V = q*Ef*d ----- Replacing F from (1)
V = Ef*d --------- canceling q

The electric field Ef is given in units of eV/Å.
This means that if you want a potential difference of 3V across your unit cell of 12Å length...

karthik_hj
Newbie
Newbie
Posts: 23
Joined: Wed Jul 20, 2022 2:24 pm

Re: Voltage-Current characteristics - Electric field

#5 Post by karthik_hj » Sat Jul 30, 2022 4:35 am

So an equivalent of 3V across 12Å would be ;

= 3V/12Å
= 0.25V/Å OR 0.25eV/Å

Im a little confused between the units

henrique_miranda
Global Moderator
Global Moderator
Posts: 414
Joined: Mon Nov 04, 2019 12:41 pm
Contact:

Re: Voltage-Current characteristics - Electric field

#6 Post by henrique_miranda » Sat Jul 30, 2022 7:50 am

Ok, I should probably have mentioned it but Eq. (3) is the definition of electronvolt.
Because VASP is using (mostly) atomic units then q is unity. In that case, the potential V and energy Energy are in eV.
The numeric value you want is EFIELD=0.25V/Å which corresponds to EFIELD=1.60217663e-19*0.25 eV/Å.

Post Reply