[gmx-users] REMD problem in concept

Mark Abraham Mark.Abraham at anu.edu.au
Wed Dec 3 17:19:17 CET 2008

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.


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