Pseudooptimization?

Axel akoh... at gmail.com
Tue Nov 17 20:56:20 UTC 2009


On Nov 17, 12:22 pm, Teodoro Laino <teodor... at gmail.com> wrote:
> Centering coordinates after each restart is slightly moving your system.
> This creates spurious forces (because of the presence  of the grid ->
> see old messages) and the optimization may go on over forever..
>
> Take out the CENTER_COORDINATES and everything should go in the way you
> think it should.

this will get you consistently into the same minimum, but
perhaps, one should add to this, that because of theses "ripples"
there is a limit to the accuracy of the energy of a geometry
optimization. this is a limitation of using plane waves and
does not only affect CP2k with QS.
this doesn't matter for MD, but if you are after very small
differences, it should be taken under consideration
as well as the inherent other accuracy limitations (e.g.
using DFT, basis set, BSSE, and so on). at some point small
differences are just random noise.

cheers,
    axel.

> Teo
>
> Ilya wrote:
> > Dear CP2K users.
>
> > I run into a problem few days ago.
>
> > I have performed a small (60 atoms) piece of hydrated quartz QS DFT
> > relaxation.
>
> > Cp2k could not find energy minimum at a time.
>
> > If I take optimized coordinates, put them in the input file again and
> > restart the optimization with the SCF_GUESS ATOMIC, cp2k will continue
> > optimization and will find some lower minimum.
>
> > The amount of opt steps needed to reach the minimum is much fewer. The
> > energy may differ by ~0.01 but in my case it really matters.
>
> > Launching 2-3 sequential optimizations I managed to find the exact
> > minimum value.
>
> > Anyway it looks suspicious. As it makes up a new wave function
> > approximation for an "optimized" coords the whole optimization goes in
> > a slightly different way each restart. As I got.
>
> > I tried to apply different optmizers - CG, BFGS, LBFGS. I also tried
> > to use OT, Mixing/Diag, changing SCF optimizers CG, DIIS. All those
> > influenced slightly. Still it does new optimization each restart,
> > instead of saing "nothing to do everything is optimized".
>
> > Now trying to change CUTOFF value, may be this could help.
> > The question might be stupid, I feel that the answer is simple, just
> > can't get it.
>
> > If someone have some ideas, I will appreciate you advice.
>
> > Input
>
> >  &GLOBAL
> >    PRINT_LEVEL  LOW
> >    PROJECT_NAME ps-t-11
> >    RUN_TYPE  GEO_OPT
> >    PREFERRED_FFT_LIBRARY FFTW
> >  &END GLOBAL
> >  &MOTION
> >    &GEO_OPT
> >      OPTIMIZER  CG
> >      MAX_DR 3.00000000E-04
> >      MAX_FORCE  4.50000000E-05
> >      RMS_DR    1.50000000E-04
> >      RMS_FORCE  3.00000000E-05
> >      MAX_ITER             1000
> >    &END GEO_OPT
> >  &END MOTION
> >  &FORCE_EVAL
> >    METHOD  QS
> >    &DFT
> >      BASIS_SET_FILE_NAME GTH_BASIS_SETS
> >      &SCF
> >        SCF_GUESS ATOMIC
> >        MAX_SCF            1000
> >      &END SCF
> >      &XC
> >        &XC_FUNCTIONAL  PBE
> >        &END XC_FUNCTIONAL
> >      &END XC
> >      &POISSON
> >        PERIODIC XZ
> >        POISSON_SOLVER WAVELET
> >      &END POISSON
> >    &END DFT
> >    &SUBSYS
> >      &CELL
> >       ABC     9.8724 25.0 10.08094
> >     UNITS  ANGSTROM
> >        PERIODIC  XZ
> >      &END CELL
> >      &KIND Si
> >        BASIS_SET TZVP-GTH
> >        POTENTIAL GTH-PBE-q4
> >      &END KIND
> >      &KIND O
> >        BASIS_SET TZVP-GTH
> >        POTENTIAL GTH-PBE-q6
> >      &END KIND
> >      &KIND C
> >        BASIS_SET TZVP-GTH
> >        POTENTIAL GTH-PBE-q4
> >      &END KIND
> >      &KIND B
> >        BASIS_SET TZVPP-GTH
> >        POTENTIAL GTH-PBE-q3
> >      &END KIND
> >      &KIND H
> >        BASIS_SET TZVP-GTH
> >        POTENTIAL GTH-PBE-q1
> >      &END KIND
> >      &TOPOLOGY
> >        COORD_FILE_FORMAT XYZ
> >        COORD_FILE_NAME /home/kupchenko/job/ps/t/ps.xyz
> >        CENTER_COORDINATES  T
> >      &END TOPOLOGY
> >    &END SUBSYS
> >  &END FORCE_EVAL
>
> > Coordinate file ps.xyz:
>
> >       60
> >  i =        1, E =      -570.7446060489
> >   H         1.2164405235       15.4842136302        0.4143744831
> >   H         6.1121896899       15.5038087647        0.4144334876
> >   H         1.2707602262       15.3655789278        5.4048093021
> >   H         6.1271079554       15.4026946050        5.4235580700
> >   O         0.4551586659       15.1183862048        0.9207263709
> >   O         5.3651001781       15.1154121407        0.9229189539
> >   O         0.5077183637       15.1235599574        5.9915222988
> >   O         5.3762635138       15.1158339064        6.0005346429
> >   H         3.8570937184       15.1545145022        5.1023747623
> >   H         8.8344418767       15.1584752804        5.0833260666
> >   H         3.8786236331       15.1947700953       10.3189982581
> >   H         8.8423420430       15.2102731172       10.2764809174
> >   O         3.0957286169       14.9472184410        4.5045744980
> >   O         8.0582595943       14.9554451515        4.5037182386
> >   O         3.0983543419       14.9962628173        9.7165567981
> >   O         8.0637432247       15.0292909929        9.6668423665
> >   O         2.4682398721       13.9468761359        2.1126453081
> >   O         7.4016859412       13.9535260868        2.1076981879
> >   O         2.4331459358       13.9452444285        7.4094370497
> >   O         7.3474209604       13.9487720010        7.3996943622
> >  Si         0.9174823157       13.6452453328        1.6331964708
> >  Si         5.8506776815       13.6460140438        1.6312922823
> >  Si         0.8945731285       13.7654223514        6.8801727781
> >  Si         5.8090768385       13.7639843442        6.8815442106
> >  Si         3.3445442865       13.6624717732        3.4584593898
> >  Si         8.2735277184       13.6625861281        3.4589630814
> >  Si         3.3211393429       13.6848373669        8.7566224332
> >  Si         8.2481557358       13.6840992310        8.7402594584
> >   O         4.9261822520       13.4850120463        3.0058435744
> >   O         9.8492612051       13.4823424700        2.9989183455
> >   O         4.8578563490       13.4964580997        8.1955274091
> >   O         9.7798690555       13.4911169759        8.1692673736
> >   O         0.8797033120       12.3830946804        0.6001141356
> >   O         5.7933420692       12.3831395817        0.6001632671
> >   O         0.8817757579       12.3795984391        6.0019735587
> >   O         5.7953154313       12.3796068132        6.0019844251
> >   O         2.7873912363       12.2645536217        4.1156930416
> >   O         7.7011498729       12.2647096129        4.1156209075
> >   O         2.8124720845       12.2891736146        9.5066763280
> >   O         7.7263380707       12.2894528459        9.5065558302
> >  Si         1.8767330997       11.4234259421       -0.2249206571
> >  Si         6.7904244881       11.4233716970       -0.2249530592
> >  Si         1.8906925923       11.4346717365        5.1661113227
> >  Si         6.8044045172       11.4346717256        5.1660918387
> >   O         2.8683800441       10.6886833092        0.8130047883
> >   O         7.7820554561       10.6886976079        0.8130092380
> >   O         2.8661225434       10.6907181430        6.2154513092
> >   O         7.7798155302       10.6907252061        6.2154563221
> >   O         0.9993480464       10.3826593668        4.3304611630
> >   O         5.9130553067       10.3826768100        4.3304808739
> >   O         0.9879650764       10.3694140533        9.7308331231
> >   O         5.9016086863       10.3694428080        9.7308465605
> >   H         2.5220936594        9.9015909978        1.2556566675
> >   H         7.4361354814        9.8984291273        1.2500346062
> >   H         3.8152371223       10.6874649056        5.9934984006
> >   H         8.7297691935       10.6932243995        5.9965260796
> >   H         1.3674986990        9.4962228514        4.1919909263
> >   H         6.2998681174        9.5107427878        4.1552631113
> >   H         0.0234329886       10.3965414804        9.7770309728
> >   H         4.9370093473       10.3979787214        9.7924189287
>
> > --
>
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