[gmx-users] How to set up constraint distcance pulling

[xiaowu759]

Dear gmxers,
 I am performing COM pulling using GMX4.0.7, to obtain the PMF as a function of distance between the COMs of two molecules. However, quite strange resuluts are generated, i.e., the distance can not be fixed at the value defined by pull_init1. The pull opinions are given below. Could you please tell me how to deal with this? Thanks a lot for any reply.
 Chaofu Wu
  
 ;Pull opinions
 pull                          = constraint
pull_geometry          = distance
;pull_dim                 = Y Y Y
pull_group0              = r1
pull_group1              = r2
pull_nstxout             = 0
pull_nstfout              = 5
 pull_init1                  = 0.80
  ------------------
   Department of Chemistry and Materials Science

 Hunan University of Humanities, Science and Technology, 
 Loudi 417000, the People's Republic of China (P.R. China)
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