[gmx-users] pull direction

[Weihua Li]

Hi all,
  Now i am confused about another problem.I will pull the substrate along a certain channel.And i want to put the direction of the channel on z axis.But i don't know how to guarantee the direction of the channel to be the z axis. Below is my pull.ppa file.
  verbose = yes
  runtype = AFM
  group_1 = Drg ;the substrate
  reference_group = protein
  reftype = com
  reflag  = 1
  direction = 0 0 1.0
  reverse = from_reference
  pullrate = 0.00004 
  forceconstant = 500
 i used the EDITCONF -rotate command to adjust the box direction.The channel direction looks to be at z axis.But how can i know the channel direction to exactly be z-axis?
 Could anyone give me some advice?
                                   
Cheers,
Weihua Li