Non symmetry inversion with fix efield

Dear all:

i´m new on lammps and i could calculate properties of argon with this program. The problem i am trying to solve now is put an sphere and move it with and electric field (easy task… ¿?). When i put an positive electric field the sphere moves with a given velocity and when i put an negative electric field the sphere moves with otrer much lower velocity. I have a problem with the ensemble i use, i suppose (nvt o nve) but i spent a lot of time trying to solve and i couldn´t solve it yet.Help is really appreciated !!!

I put the code i use

units lj
atom_style charge
lattice fcc 1

region laurabox block -100 100 -100 1000 -1000 1000
create_box 1 laurabox

region filament sphere 0 0 0 2

create_atoms 1 region filament
mass 1 1.0
set atom 1 charge -2.0

#------------ kspace_style ewald 1.0e-3

pair_style lj/cut 2.5
pair_coeff 1 1 1 1 6.05

group mid region filament

velocity mid zero linear

neighbor 0.3 bin
neigh_modify every 20 delay 0 check no

#------------ fix 1 all nvt temp 393.15 393.15 100.0
#------------ Pongo campo para un lado

fix 22 all efield 0.0 0.0 -20

fix 1 all nve

dump id all atom 50 dump.titi030.9
timestep 0.01

thermo 100
run 2000

#------------ fix 22 all efield 0.0 0.0 -20
#------------ run 2000

Thank you so much !!!

Mg. Néstor Ghenzi
Centro Atómico Constituyentes
1650 Buenos Aires
Tel: +541167727102
[[email protected]](mailto:[email protected])

[[email protected]](mailto:[email protected])

I imagine you want to use an NVE ensemble for this.
Other than that, I don't understand your question.
You have to be more specific than, my simulation
doesn't work - why?