[CP2K:888] Re: Variable cell optimization

[Nichols A. Romero]

Rad,

For a material like diamond, a fluctuation of 50 kbar should be expected
(even larger). That's only 5 GPa.

My experience with DFT is that converging the pressure to less than 1 kbar
is unrealistic. So worrying about
bars is a waste of time. The story is probably different for interatomic
potential-based calculations. I cannot
comment on those.

On Wed, Mar 26, 2008 at 4:36 PM, Teodoro Laino <teodor... at gmail.com>
wrote:

>
> Rad,
>
> On 26 Mar 2008, at 21:20, Rad wrote:
>
> >
> > Teo,
> >
> > Couple of feedback: the volume is printed in Angstrom in some places
> > and bohr in other places. Is it possible to sick to one unit (just
> > bohr) so that post processing scripts people set up can stay as they
> > are?
> the .cell file is always in ANGSTROM. the output on the screen is
> according the unit that you
> specified in your input file (if you use angstrom you will get
> angstrom, if you use bohr you will get bohr)..
> Use the .cell file for post-processing if you don't like the idea
> that the output depends on the unit that
> you decide to use.
>
> > The output produces a bunch of restart files for wavefunction and
> > Restart*restart. (this is for the case of GEO_OPT option). When I
> > restart the calculation which one I should use?
> The files generated during the geometry optimization are tagged *-
> GEO_OPT-*..
> you should also have a normal restart file without the -GEO_OPT-..
> use that one!
> In case you do MD instead of GEO_OPT you will find MD.
>
> > As usual convergence is always a tricky one. I am trying small systems
> > and having issues with pressure fluctuating wildly, starting with few
> > bars and reaching 50 kbars withing few steps. I will do few more runs
> > (QS, GPW) and get back to you on this. The second item is the one I
> > need a response before restarting my calculations.
> Rad, for material that are quite hard of course small variations of
> the cell have large fluctuations in the pressure.
> You can play with the bunch of parameters of the CELL_OPT section
> (specifically with the LS 2PNT for reducing
> the max_allowed_step) to get a safer optimization..
>
> Teo
>
> >
> > Thanks a lot for this most anticipated module for our team.
> >
> > Rad
> >
> > On Mar 25, 9:03 am, Rad <rad.... at arl.army.mil> wrote:
> >> Thanks Teo,
> >>
> >> I just got back from my vacation and it is a great news. I will
> >> get to
> >> it immediately as I am working on several systems for which this
> >> method would be ideal.
> >>
> >> Rad
> >>
> >> On Mar 20, 8:50 pm, Teodoro Laino <teodor... at gmail.com> wrote:
> >>
> >>
> >>
> >>> Hi Rad,
> >>
> >>> just a follow up about this message.
> >>> Me and Paolo Raiteri implemented the cell optimization algorithm in
> >>> cp2k both at 0K (optimizing the atomic positions) and at finite
> >>> temperature (averaging the stress tensor over an MD run). There
> >>> are a
> >>> couple of regtest added in Fist/regtest-12/argon* showing how to use
> >>> the cell optimization algorithm. At the moment the only scheme
> >>> available is the CG with a 2PNT line search (quite efficient in the
> >>> systems
> >>> I tested).
> >>> Comments and suggestion are, as usual, welcome.
> >>
> >>> Ciao
> >>> Teo
> >>
> >>> On 17 Oct 2007, at 21:51, Rad wrote:
> >>
> >>>> Hi everybody,
> >>
> >>>> Is it possible to do variable cell optimization using CP2K? Can
> >>>> somebody provide me with a sample input section for that?
> >>
> >>>> Thanks
> >>
> >>>> Rad- Hide quoted text -
> >>
> >>> - Show quoted text -- Hide quoted text -
> >>
> >> - Show quoted text -
> > >
>
>
> >
>


-- 
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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