[CP2K-user] [CP2K:12049] Re: Cell Optimization does not work in QM

[Pierre Cazade]

Dear Dirk,

Thank you for your answer. I went through the tutorial about CUTOFF and 
RELCUTOFF. That's how I came up with CUTOFF=1400 and RELCUTOFF=80. I 
also tried CUTOFF=400 and RELCUTOFF=60. It does not change the problem 
when it comes to the cell optimization. Furthermore, I have, to some 
extend, a similar issue on the large crystal using DFTB. Please have a 
look at the input files, there might be a silly mistake I make or a 
missing keyword, I am not aware of.

Regarding the tutorial, it is far from being helpful as the criterion to 
decide if CUTOFF and RELCUTOFF are appropriate is rather 
undefined/unspecific. Anyway, I have exhausted the resources available 
on CP2K website before asking on the forum.

Thanks again,
Pierre

On 07/08/2019 17:26, Dr. Dirk Buddensiek wrote:
> Dear Pierre,
> at first glance the CUTOFF and RELCUTOFF seem to be a lttle bit 
> unbalanced. Maybe it would help to take a look in the tutorial hpw to 
> get optimised cuttof values. https://www.cp2k.org/howto:converging_cutoff
>
> Am Mittwoch, 7. August 2019 17:05:56 UTC+2 schrieb Pierre-André Cazade:
>
>     Hello,
>
>     I am rather new to CP2K though I am experienced with molecular
>     modelling both quantum and classical, and with a wide range of
>     software. It is quite frustrating that it seems impossible to get
>     CP2K to perform a simple CELL_OPT of a beta glycine crystal (20
>     atoms, monoclinic) with PBE. Such a calculation works fine with
>     VASP, so I am quite surprised the same calculation goes astray
>     with CP2K. Basically, the B unit cell vector increases drastically
>     up to absurd values. Needless to say, this is a test system as I
>     wish to use CP2K for its linear scaling DFT to model protein
>     crystals. I have tried to play with CUTOFF and REL_CUTOFF in the
>     MGRID section up to 1400 and 80 respectively. I also tried GPW and
>     GAPW methods, all electrons or GTH pseudo. Nothing works. Please,
>     if anyone could have a look at the attached input file
>     "cell_opt_qm.inp" and point what's wrong in it, I would be grateful.
>
>     Furthermore, I have tried LS approach with DFTB on a 5x5x5 crystal
>     of beta glycine and do not have much more success. First, the
>     pressure in the crystal is insanely high and will lead again to a
>     20 folds increase of the lattice vectors (with CG). Then, with
>     LBFGS method, the system stops after 3 to 4 cycles with a message
>     telling LBFGS convergence criteria were reached, whereas the
>     system is clearly not. Again, I would be grateful if anyone could
>     tell me what's wrong with my system ("cell_opt2_qm.inp" with
>     "betacry.pdb" for the coordinates). Ideally, my goal would be to
>     be able to run large complex systems with the LS approach and with
>     any DFT/DFTB method.
>
>     Thank you in advance for your help.
>
>     Regards,
>     Pierre
>
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-- 
Dr Pierre Cazade, PhD
AD3-023, Bernal Institute,
University of Limerick,
Plassey Park Road,
Castletroy, co. Limerick,
Ireland

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