[CP2K:765] Re: nose thermostat

[Nichols A. Romero]

To elaborate on what Teo said, (he can correct me if I am wrong)

In NVT, the total energy of the *real sytem + thermostat* should be
conserved.
(I don't remember if CP2K outputs this quantity, but most codes should).

The total energy of just the real system (atoms,molecules,etc.) should have
a mean value (after equilibration) with fluctuations proportional to
1/sqrt(N) (or something like that).

If the total energy of the real system increases or decreases without
bounds, then there is something wrong.
Or maybe you are near some phase transition.

On Mon, Mar 10, 2008 at 4:37 PM, Teodoro Laino <teodor... at gmail.com>
wrote:

>
> Ciao Diederica,
>
> >
> > These are added, as an attachment this time
>
> Thanks.. will look into this problem ASAP.
>
> > I'm modelling an isolated molecule, it should fit in the box. Using
> > NVE without temperature rescaling, with an analogue structure, an
> > energy drift was observed, that got worse after about 20 ps, though
> > no non-convergence was observed. The input file and an energy-plot
> > are added.
> If you have a drift with NVE this means that energy and forces are
> not consistent.. or (what I assume) that the cutoff for the coulomb
> interactions is not large enough..
>
> Please put all of the  RC_COULOMB and RC_INTERACTION and RC_RANGE to
> 50.0.
> You've the problem that in your cell the standard range (24 bohr)
> does not fully cover the extension of your molecule (more than 26 bohr).
> Use a larger box (30.0 Angstrom) and set the above keywords to 50.0
> bohr.
> You should not see any jump in the energy (or drift)..
>
> > The potential and kinetic energy are conserved indeed, but the
> > conserved quantity is not
> Sorry to disprove you, but it is not possible that in an NVT you have
> kinetic and potential conserved, since the thermostat
> is continuously exchanging energy with the system.  I't s a matter of
> concept.. we may discuss about the magnitude of the
> thermostat energy.. but that's another story..
>
> Cheers
> teo
>
>
>
> >
> >
> >
> > For the next time, can you please put tables and input files as
> > attachment (maybe .tgz) so that the formatting of mail readers are
> > not changed and the input files not digested ? Thanks..
> >
> > Ciao,
> > teo
> >
> > Thanks for helping!
> >
> > Greetz,
> > Diederica
> >
> >
> >
> >
> > >
> > <mailcp2k.tgz>
>
>
> >
>


-- 
Nichols A. Romero, Ph.D.
DoD User Productivity Enhancement and Technology Transfer (PET) Group
High Performance Technologies, Inc.
Reston, VA
443-567-8328 (C)
410-278-2692 (O)
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