[gmx-users] REMD temperature spacing error

[Mark Abraham]

k is dimensionless. It does not relate to Boltzmann's constant. The
exponential spacing it produces would lead to replica exchange rates that
are constant over the T range, under certain assumptions (e.g. papers by
David A Kofke). In practice, it normally would not lead to such rates.
Whether constant exchange rate is even useful/meaningful is another matter
(e.g. papers by Walter Nadler & Ulrich Hansmann).

Mark

On Wed, Mar 13, 2013 at 12:49 PM, Nikunj Maheshwari <
nixcrazyforher at gmail.com> wrote:

> I think determining k in the equation is not clear. How is it related to a
> system size? If k=1/(kb.t) [kb=boltzmann constt], then for a given starting
> temperature, the temp. spacing will be the same. Is that correct?
>
> On Wed, Mar 13, 2013 at 5:02 PM, Mark Abraham <mark.j.abraham at gmail.com
> >wrote:
>
> > On Wed, Mar 13, 2013 at 11:24 AM, Nikunj Maheshwari <
> > nixcrazyforher at gmail.com> wrote:
> >
> > > Dear all.
> > >
> > > We are trying to run REMD on two proteins : 292 and 44 aa residues
> using
> > > GROMACS 4.6.
> > > We are unable to obtain the temperature spacing using REMD temperature
> > > generator (http://folding.bmc.uu.se/remd/) as it is giving myriad
> > > temperature ranges (in the order of 150 for 250-550K range)
> > >
> >
> > Sounds normal for the kind of system you seem to have. Higher numbers of
> > degrees of freedom require closer temperature spacing.
> >
> > Is there any other way to determine the spacing? Can the equation
> > > T(i)=T(0).e(k.i) be used, as we are unable to comprehend it?
> > >
> >
> > Yes, but if you want exchanges to occur, there are constraints on the
> size
> > of k. What's so hard about T(i+1)=T(i)*k?
> >
> > Mark
> > --
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