Re: WHAM analysis for Umbrella sampling

From: Chris Chipot (chipot_at_ks.uiuc.edu)
Date: Wed May 01 2013 - 02:01:44 CDT

Ada,

I suggest that you have a look at the original Kumar et al. paper from 1992
(and possibly the earlier work of Bob Swendsen). There, you will see that
the only thing needed to solve the WHAM (Ferrenberg-Swendsen) equations
is your biased probability distributions in the different strata of your
reaction
path and the biasing potentials that you have used in these different
strata.
Period. This is also spelled out in Benoit Roux's 1995 paper on potential of
mean force calculations.

Chris Chipot

On 5/1/13 12:18 AM, Ada Zhan wrote:
> Hi there,
>
> Thanks for all your responses!
>
> Jerome, are you using WHAM from Grossfield lab? That is what I am using.
> According to their WHAM manual, time series files are required to
> contain the information of time and positions. And their commands
> process the time series files as the starting point.
> I understand they are processing the time series files into histograms
> or counts that will be implemented into the WHAM equations.
> My curiosity would be how to direcetly implement NAMD generated
> histograms into existing WHAM software without modifing their codes.
>
> Thanks!
>
> Best regards,
> Ada
>
> > Date: Tue, 30 Apr 2013 11:07:52 +0200
> > From: jerome.henin_at_ibpc.fr
> > To: broomsday_at_gmail.com
> > CC: namd-l_at_ks.uiuc.edu; zyqfrog10_at_msn.com
> > Subject: Re: namd-l: WHAM analysis for Umbrella sampling
> >
> > Hi,
> >
> > I recommended the histogram solution to avoid the downsampling that
> happens in the trajectory. Apparently your implementation of WHAM
> requires a trajectory, I am not sure why. One possible advantage of
> saving a trajectory is that it is not discretized in colvar space, so
> you can optimize the binning width afterwards. If the histogram is
> fine enough though, that's not a problem.
> >
> > Cheers,
> > Jerome
> >
> >
> > ----- Original Message -----
> > >
> > > yeah you don't do the histogram thing. You just want the
> > > .colvars.traj files.
> > >
> > >
> > >
> > >
> > > On Mon, Apr 29, 2013 at 3:41 PM, Ada Zhan < zyqfrog10_at_msn.com >
> > > wrote:
> > >
> > >
> > >
> > >
> > > Hi there,
> > >
> > > I want to perform WHAM analysis on histogram files generated from
> > > umbrella sampling simulations.
> > >
> > > According to WHAM instructions, time series files contain the
> > > information of time and position that are recorded in the .traj
> > > files.
> > > Now I used 'histogram' function provided by colvars. How do I use
> > > these histogram .dat files for WHAM use? Do they serve as time
> > > series files also? Or we use them somewhere differently? If we put
> > > them in the field of time series files, how would WHAM process them
> > > since the meaning of the provided information is totally changed?
> > >
> > > Thanks!
> > >
> > > Best regards,
> > > Ada
> > >
> > >
> > >
> > > --
> > > Aron Broom M.Sc
> > > PhD Student
> > > Department of Chemistry
> > > University of Waterloo
> > >

-- 
_______________________________________________________________________
Chris Chipot, Ph.D.
Theoretical and Computational Biophysics Group
Beckman Institute
University of Illinois at Urbana-Champaign
405 North Mathews                                 Phone: (217) 244-5711
Urbana, Illinois 61801                            Fax:   (217) 244-6078
                             E-mail: chipot_at_ks.uiuc.edu
                                     Christophe.Chipot_at_edam.uhp-nancy.fr
                             Web:    http://www.ks.uiuc.edu/~chipot
                                     http://www.edam.uhp-nancy.fr
The light shines in the darkness, and the darkness has not overcome it.
                                                               John 1:5.
_______________________________________________________________________

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