Voltage-Current characteristics - Electric field

[karthik_hj]

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]

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]

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]

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]

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]

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.