[Pw_forum] Dynamic Temperature Control and Select Stationary Ions.

[Nicola Marzari]

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