[Pw_forum] Dynamic Temperature Control and Select Stationary Ions.

[Tim Teatro]

Dear Nicola,

Thank you for your reply. I am working on large clusters, so
calculation time is not a problem. Unfortunately I will not have
access to cp.x for a few days because the computer cluster on which I
was able to compile it is down. Therefore, I will need to use pw.x for
now.

Could you give me a list of input parameters I would need for changing
the temperature during a MD simulation, and for holding a few specific
ions still while others are able to move? It seems I can only find
references to temperature rescaling and the Nose thermostat, which
require the temperature to be specified ahead of time. And of course I
can turn the ion dynamics off easily enough, but not for certain
atoms.

If you have any examples, this would be great too.

Thanks again.

Cheers.

On 6/10/06, Nicola Marzari <marzari at mit.edu> wrote:
>
>
> Dear Tim,
>
>
> you can do this both with CP or PWSCF. CP would be the ideal code,
> provided the system remains insulating.
> On a single state-of-thje-art Pentium I think you can get nowadays
> 1ps/day, for a system with ~250 electrons.
>
> Otherwise, you should use Born-Oppenheimer dynamics (that is the
> standard mode for PWSCF, and is
> available as an option in CP).
>
> Melting and quenching has been used often - you could look e.g. at the
> works by Alfredo Pasquarello at EPFL (especially
> from the ~1998 Nature on SiO2 onwards).
>
> Car-Parrinello MD, and to a certain extent Born-Oppenheimer MD, require
> a good understanding of several concepts -
> we'll run a school on "Ab-initio molecular dynamics" in
> Urbana-Champaign, at the beginning of
> August, and attending that would probably be very useful:
> http://www.mcc.uiuc.edu/summerschool/2006/
>
> At a minimum, have a close look at the review papers on the web -
> especially the one
> by Marx and Hutter
> (http://www.theochem.ruhr-uni-bochum.de/research/marx/cprev.en.html) or the
> shorter one by Galli and Pasquarello. The RevModPhys review of Payne
> from 1992 is another very
> good reference. As a word of care, look also at the 2002 and 2004 JCP
> from Tangney/Scandolo and
> from the Galli group.
>
>
>              nicola
>
>
>
>
>
>
>
> Tim Teatro wrote:
> > Hello.
> >
> > I believe I posted a similar question a year or two ago, but A) I
> > don't think the question was resolved and B) the code has changed, so
> > perhaps what was once a problem is not now.
> >
> > My group has a situation where we need to melt a crystal system, and
> > then cool it back down to make an amorphous structure. Is this
> > possible using any of the codes in the ESPRESSO package?
> >
> > If so, how? Do you happen to have an input example?
> >
> > Also, we have another system in which it would be useful to hold
> > certain ions stationary while others are free to move under the Verlet
> > algorithm. Of course we could cheat and set the mass of these atoms to
> > be extremely high, but I think it would be better to simply stop them
> > completely.
> >
> > Thank you for your time.
> >
> > --
> > Timothy A.V. Teatro
> > University of Ontario Institute of Technology
> > e.  timtro at gmail.com <mailto:timtro at gmail.com>
> > p.  905.579.9248
> > c.  905.442.9248
>
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-- 
Timothy A.V. Teatro
University of Ontario Institute of Technology
e.  timtro at gmail.com
p.  905.579.9248
c.  905.442.9248