[gmx-users] Electric field applied to a water box

[Nidhin Thomas]

Dear all,

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 = (4 x 4 x 4) nm
Final Size     = (4.3 x 2.8 x 4.9) nm

I would like to know if I made an error in providing the mdp options and also the origin of the compression of water box in Y direction.

Thanks a lot for your help!.

Nidhin Thomas
University of Houston