[gmx-users] REMD problem in concept

Berk Hess gmx3 at hotmail.com
Wed Dec 3 17:25:09 CET 2008


I think you are talking about two different concepts.
At the moment of switching the replicas, the potential energy
does not change, because the force field is temperature indepent.
This is what Chris meant.
As the system evolves in time, the potential energy will go up
when a replica is switched to a higher temperature.


> Date: Thu, 4 Dec 2008 03:19:17 +1100
> From: Mark.Abraham at anu.edu.au
> To: gmx-users at gromacs.org
> Subject: Re: [gmx-users] REMD problem in concept
> chris.neale at utoronto.ca wrote:
> > dG=dH-TdS
> > 
> > so as T increases, so does the entropic contribution to the free energy 
> > (=available energy). The potential energies stay the same when using a 
> > temperature-independent forcefield (like all of the ones that come with 
> > gromacs).
> That's not quite right. The average total energy (H, above) increases 
> with T, and the equipartition theorem requires that for a typical MD 
> system in thermal equilibrium, some of that energy must go to increased 
> average PE. The form of the forcefield doesn't change, of course. This 
> KE-PE-TE behaviour can be readily observed in an REMD simulation and is 
> documented in various graphs in various REMD papers.
> > Your system will easily cross barriers on the order of KbT and thus 
> > barriers are more easily crossed at higher temperature.
>  >
> > Nearly every RE paper has an introductory section that goes over these 
> > topics in more or less detail. I suggest that you read the introduction 
> > and theory sections of about 10 of them and you should by then 
> > understand it very well.
> Yep, agreed.
> Mark
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