[gmx-users] External electric field applied to water box

[Justin Lemkul]

On 5/19/19 11:32 PM, Nidhin Thomas wrote:
> Hello GROMACS users,
>
> I tried to apply a static electric field across a water box. I used  anisotropic pressure coupling. Details of the pressure coupling is given below.
>
> pcoupl                  = Parrinello-Rahman
> pcoupltype              = anisotropic
> tau_p                   = 5.0
> compressibility         = 4.5e-5 4.5e-5 4.5e-5 0 0 0
> ref_p                   = 1.0 1.0 1.0 0 0 0
> ;
> constraints             = h-bonds
> constraint_algorithm    = LINCS
> continuation            = yes
> ;
> electric-field-y = 0.1 0 0 0
>
> I see that water box size reduced in the direction of application of electric field (Y) and increased in X and Z direction.
>
> Original Size = (3.90 x 3.90 x 3.90) nm
> Final Size     = (4.39 x 2.66 x 5.16) nm
>
> Could someone please help me understand why the water box is shrinking in the direction of electric field ? can someone please let me know how external electric field is actually implemented in GROMACS ?

Anisotropic pressure coupling intrinsically leads to the distortion of 
the box shape. Run a control simulation of water with no electric field 
and you will see the same thing.

-Justin

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Justin A. Lemkul, Ph.D.
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