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

[Matt W]

Standard inputs are in Angstroms for a coord section.

The most common problem is that the planewave basis changes as the cell 
optimizes. You can use a constant size of plane wave basis by specifying a 
reference cell, something like this. Where the CELL_REF contains a 
reference cell that should be a bit bigger that the expected largest cell 
after optimization.

    &CELL
      ABC 5.620 5.620 5.620
      &CELL_REF
        ABC 5.620*1.1 5.620*1.1 5.620*1.1
      &END
    &END CELL

If your cell has symmetry (orthorhombic, hexagonal etc) you can specify 
this to be kept. Similarly first optimizing just the volume and keeping the 
angles constant, then relaxing everything can be more efficient.

Also I'd stick with BFGS rather than LBFGS unless you system is huge (> 
2000 atoms)

Maybe this helps a little, 

Matt


On Thursday, August 8, 2019 at 10:46:18 AM UTC+1, Dr. Dirk Buddensiek wrote:
>
> Hi Pierre,
>
> good luck. Concerning distance units: It might be that there are in Bohr 
> for MP2. But you can set the units explicitly in the input deck.
> Dirk
>
> 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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