Confusion: cation and anion move towards the same direction under an external electric field

[Marcella Iannuzzi]

Hi,

this external potential is not an electric field, it is just a linear 
potential.
Check the keywords EFIELD and PERIODIC_EFIELD.

Marcella

On Wednesday, July 19, 2017 at 12:20:54 PM UTC+2, Tonys_Yu wrote:
>
> Hello,
>        I want to study a ionic displacement in a bulk water box with 30 
> water molecules. External electric field is 0.1V/A, and added by 
> EXTERNAL_POTENTIAL command as below:
>
>       &EXTERNAL_POTENTIAL
>        FUNCTION (A/B)*X
>        PARAMETERS A B
>        VALUES [eV] 1.0 [angstrom] 10.0
>       &END EXTERNAL_POTENTIAL
>
>     What makes me confused is that both water molecules and K-ion are 
> moving along the negative direction of X. Moreover, when I changed the 
> K-ion by a Cl-ion or reduced the electric field to a smaller value 
> (0.001V/A), the same results was observed. It seems contrary to the fact 
> that, with the same electric field (value and direction), K-ion and Cl-ion 
> would move towards opposite directions. 
>     I beg someone could shed light on my confusion. Necessary files have 
> been attached.
>
> Tonys Yu
>
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