[gmx-users] Poor sampling in PMF at some points

[Alex]

Dear gromacs user,

In my PMF calculation by umbrella sampling in z direction, I have surely
considered some windows or configuration in

z= "... 1.878, 1.886,  1.891, 1.902, 1.911, 1.932, 1.949, 1.959, 1.961
...",

but I do not know why I have poor sampling in the some point which are
really close to the above points which I had considered configuration for
them?

for example :
WARNING, no data point in bin 22 (z=1.89414)

WARNING, no data point in bin 23 (z=1.91285)

WARNING, no data point in bin 24 (z=1.93156)

WARNING, no data point in bin 25 (z=1.95026)

WARNING, no data point in bin 26 (z=1.96897)


Here is my pull part of mdp file which run for 30 ns for each windows:
-----------------
pull                     = yes
pull-ngroups             = 2
pull-ncoords             = 1
pull-group1-name         = Protein
pull-group2-name         = Other

pull-coord1-groups       = 1 2
pull-coord1-type         = umbrella
pull-coord1-dim          = N N Y
pull-coord1-start        = yes
pull-coord1-rate         = 0.0
pull-coord1-geometry     = distance
pull-coord1-k            = 1500   ;;kJ/(mol nm^2)
pull-print-components    = Yes
pull-nstxout             = 1000
pull-nstfout             = 1000
pull-print-com1          = yes
-------------

Thanks

Regards,
Alex