On 1/1/13 11:48 PM, ramesh cheerla wrote:
Dear Gromacs users,
I am performing umbrella sampling
simulations by selecting configurations with spacing window of 0.02nm from
pulling simulations with the following options in .mdp file to get PMF
along a axis for permeation of ion through a channel.
; Pull code
pull = umbrella
pull_geometry = position ; simple distance increase
pull_dim = N Y N
pull_vec1 = 0 -1 0
pull_start = yes ; define initial COM distance > 0
pull_ngroups = 1
pull_group0 = FIXEDATOM
pull_group1 = SMDATOM
pull_rate1 = 0.0 ; 0.01 nm per ps = 10 nm per ns
pull_k1 = 2000 ; kJ mol^-1 nm^-2
pull_init1 = 0
And am using g_wham to get PMF, while using g_wham, am getting the
warnings like :
WARNING, no data point in bin 139 (z=-0.492557) !
You may not get a reasonable profile. Check your histograms!
Warning, poor sampling bin 193 (z=-0.364322). Check your histograms!
Warning, poor sampling bin 194 (z=-0.361947). Check your histograms!
Warning, poor sampling bin 195 (z=-0.359572). Check your histograms!
Warning, poor sampling bin 196 (z=-0.357197). Check your histograms!
Warning, poor sampling bin 197 (z=-0.354823). Check your histograms!
Warning, poor sampling bin 198 (z=-0.352448). Check your histograms!
Warning, poor sampling bin 199 (z=-0.350073). Check your histograms!
Initialized rapid wham stuff (contrib tolerance 6.66667e-08)
Evaluating only 2115 of 3000 expressions.
I have checked my histograms and PMF profile, by doing so I have understood
that histograms overlapping is restricted to only some regions and there is
no histograms at all in some regions i.e severe sampling problems at
barrier regions. here I am sending the link that containing PMF profile
that I have obtained, http://researchweb.iiit.ac.in/~bipin.singh/pmf.jpg
Can anybody tell me how can I get proper sampling at barrier regions is
there any efficient way to do this, how about meta dynamics with suitable
CV (collective variable) ? .
Use a stronger force constant in these barrier regions to restrict the movement
along the reaction coordinate.
-Justin
--
========================================
Justin A. Lemkul, Ph.D.
Research Scientist
Department of Biochemistry
Virginia Tech
Blacksburg, VA
jalemkul[at]vt.edu | (540) 231-9080
http://www.bevanlab.biochem.vt.edu/Pages/Personal/justin
========================================
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