[gmx-users] how to pull both direction with constant force

[Md. Imrul Reza Shishir]

Dear all
In pull code simulation i want pull my system with constant force pulling
in both direction.
In the below i applied a position restrain at group 1 and pull with
constant force the outher group.
but know i want apply constant force pulling in both direction. I want your
suggestion how should I change the below code.

; Pull code
pull                    = yes
pull_ngroups            = 2
pull_ncoords            = 1
pull_group1_name        = Pos_B
pull_group2_name        = Pos_A
pull_coord1_type        = constant-force ; harmonic biasing force
pull_coord1_geometry    = distance      ; simple distance increase
pull_coord1_groups      = 1 2
pull_coord1_dim         = N N Y
pull_coord1_k           = -7000          ; kJ mol^-1 nm^-1
pull_coord1_start       = yes           ; define initial COM distance > 0

-- 
*Md Imrul Reza Shishir*
Master Student
*Inha University*
*CRC for NanoCellulose Future Composites*
36 Getbeol-ro, Yeonsu-gu
Incheon 21999
South Korea