[Pw_forum] Dynamic Temperature Control and Select Stationary Ions.

[Yonas Abraham]

Dear Tim,

In CP (QE >= 3), there is a way to change temperature
on the fly  during the MD simulation. look at
Doc/AUTOPILOT file on how to  use it. In fact, it will
let you change up to 10 CP (like dt, isave, iprint
etc)  variables on the fly. in addition, you can even
PAUSE the simulation while you are deciding what value
to use!

but the current AUTOPILOT implementation doesn't allow
you to fix certain atoms on the fly. But if you are
serious, you can extend AUTOPILOT to do so.


But I don't know if there is such thing on pw.x.   

/yonas

--- Tim Teatro <timtro at gmail.com> wrote:

> 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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> > Pw_forum at pwscf.org
> > http://www.democritos.it/mailman/listinfo/pw_forum
> >
> 
> 
> 
> -- 
> Timothy A.V. Teatro
> University of Ontario Institute of Technology
> e.  timtro at gmail.com
> p.  905.579.9248
> c.  905.442.9248
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