以下内容来源：关于gmx的pull代码 - 分子模拟 (Molecular Modeling) - 计算化学公社 (keinsci.com)
; Pull code
pull = yes ; Pull start
pull_ngroups = 2 ; The number of pull groups
pull_ncoords = 1 ; The number of pull coordinates
pull_group1_name = A ; The name of the pull group
pull_group2_name = B ; The name of the pull group （It is frozen here）
pull_coord1_type = constant-force ; Center of mass pulling using a linear potential and therefore a constant force
pull-coord1_geometry = direction-periodic ; As direction, but allows the distance to be larger than half the box size
pull_coord1_dim = Y N N ; the distance components to be used with geometry distance
pull_coord1_vec = 1.0 0.0 0.0 ; Pull direction
pull_coord1_k = 1000 ; pulling force kJ mol^-1 nm^-1
pull-coord1-groups = 1 2 ; The two groups indices should be given on which this pull coordinate will operate
pull-nstxout = 10 ; frequency for writing out the COMs of all the pull group
pull-nstfout = 1 ; frequency for writing out the force of all the pulled grou