Variable cell optimization

[Rad]

Nick,

I have done cp2k calculations with pressure fluctuation of few bars
(well after 4000 steps in an NPT ensemble). All my diamond
calculations had a fluctuation of few kbars. This one I am trying is a
molecular system and I am hoping
to have fluctuations within few kbars. If not I will have to relax my
convergence criteria. The volume of the cell also fluctuates and I am
not sure it is because of the fluctuation in the pressure or due to
other factors such as not taking
into account dispersion in molecular crystals. I am hoping that the
molcular dynamics based cell optimization will give better resulsts
and my calculations are waiting in the queue.

Rad

On Mar 26, 5:16 pm, "Nichols A. Romero" <naro... at gmail.com> wrote:
> 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)- Hide quoted text -
>
> - Show quoted text -