[gmx-users] Problems with umbrella sampling

[Amir Marcovitz]

Hi,

my system is constructed of 2 parallel plates in a box with solvent. each
plate is made of 36 atoms which are positively charged on one of them (SRP)
and negatively charged on the other plate (SRN).

i want to perform a simulation with umbrella sampling between the 2 so i
defined the pulling section parameters in the .mdp parameter file as
following:

; COM PULLING
; Pull type: no, umbrella, constraint or constant_force
pull                     = umbrella
; Pull geometry: distance, direction, cylinder or position
pull_geometry            = distance
; Select components for the pull vector. default: Y Y Y
pull_dim                 = Y Y Y
; Cylinder radius for dynamic reaction force groups (nm)
pull_r1                  = 1
; Switch from r1 to r0 in case of dynamic reaction force
pull_r0                  = 1.5
pull_constr_tol          = 1e-06
pull_start               = no
pull_nstxout             = 10
pull_nstfout             = 1
; Number of pull groups
pull_ngroups             = 2
; Group name, weight (default all 1), vector, init, rate (nm/ps),
kJ/(mol*nm^2)
pull_group0              = SRP
pull_weights0            = 1
pull_pbcatom0            = 0
pull_group1              = SRN
pull_weights1            = 1
pull_pbcatom1            = 0
pull_vec1                = 0.0 1.0 0.0
pull_init1               = 1.5
pull_rate1               = 0
pull_k1                  = 1
pull_kB1                 = 0

when proccesing the file with grompp i get the following error:

*Fatal error:
Number of weights (1) for pull group 0 'SRP' does not match the number of
atoms (36)*

is someone recognizing my mistake?
does someone has an experience with umbrella sampling in GROMACS?

thanks'
amir
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