[gmx-users] eletrical filed issue

[Tong Li]

Dear Gromacs Developers or Users

I am trying to apply a constant electrical field in Gromacs. I have made a charged fullerene in vacuum for testing. A electrical field in x direction is applied as:

; Electric field
E-x             = 1 2 1

However, the C60 moves only around 0.1 nm in 10 ps and then stops. My whole simulation period is 50 ps, in the following 40 ps, the C60 is just donging relaxation (likely). The first thing I have done is change the simulation step size from 1 fs to 0.5 fs, the simulation result is the same. Then, I have used the output conformation for another sequential simulation, then this happens again (another 0.1 nm in 10 ps). I also changed the box size to understand the surface effect of PBC, the difference is pretty small. The I removed the PBC, it didn't change, either.

I have read the manual, it says:

the first number: the number of cosines, only 1 is implemented (with frequency 0).

However, I didn't quite get this 'frequency 0'. Does this mean there is one cosine in one second? Or one cosine in the whole simulation period? Or in one simulation time step?

Another thing is I have checked the field output, it is as below. I guess this means constant force field, but not quite sure.

Thanks a lot for your help!

         0           2           0           0 #FIELD
    0.0005           2           0           0 #FIELD
     0.001           2           0           0 #FIELD
    0.0015           2           0           0 #FIELD
     0.002           2           0           0 #FIELD
    0.0025           2           0           0 #FIELD
     0.003           2           0           0 #FIELD
    0.0035           2           0           0 #FIELD
     0.004           2           0           0 #FIELD
    0.0045           2           0           0 #FIELD
     0.005           2           0           0 #FIELD
    0.0055           2           0           0 #FIELD
     0.006           2           0           0 #FIELD
    0.0065           2           0           0 #FIELD
     0.007           2           0           0 #FIELD
    0.0075           2           0           0 #FIELD
     0.008           2           0           0 #FIELD
    0.0085           2           0           0 #FIELD
     0.009           2           0           0 #FIELD
    0.0095           2           0           0 #FIELD
      0.01           2           0           0 #FIELD
    0.0105           2           0           0 #FIELD
     0.011           2           0           0 #FIELD
    0.0115           2           0           0 #FIELD
     0.012           2           0           0 #FIELD
    0.0125           2           0           0 #FIELD
     0.013           2           0           0 #FIELD
    0.0135           2           0           0 #FIELD
     0.014           2           0           0 #FIELD
    0.0145           2           0           0 #FIELD
     0.015           2           0           0 #FIELD
    0.0155           2           0           0 #FIELD
     0.016           2           0           0 #FIELD
Tong Li
email t14.li at qut.edu.au