Geometry optimisation converges to nonsense

[hfruchtl]

Folks,

I am trying to do my first baby steps with CP2K, after several aborted 
attempts, so please tell me if I do something very stupid.

One thing that worries me after first tests is that geometry optimisations 
look converged, when they clearly aren't. In the example below, I start 
something that should be a water dimer at a very wrong geometry. When I 
plot the energy changes, they become smaller as expected, and after less 
than 30 steps the program finishes. But the geometry in the xyz file looks 
nothing like I expect (H2O)2 to look. When I optimise this structure with 
the program that must not be named, using the same functional, I get a 
proper dimer. If I then plug this into CP2K, it remains close to this 
geometry (good!) with a much lower energy than the first attempt (also 
good). I understand that BFGS may not be good from a bad guess, but I would 
expect CG to get there in the end, or at least not look like it converged. 
I'd be very surprised if this was a local minimum. In short: how do I know 
if I can trust an optimised geometry?

Input below. Thanks in advance,

  Herbert

&GLOBAL
  PROJECT water-dimer
  RUN_TYPE GEO_OPT
  PRINT_LEVEL high
&END GLOBAL

&MOTION
  &GEO_OPT
    MAX_ITER 2000
    MINIMIZER CG
  &END GEO_OPT
  &PRINT
    &TRAJECTORY
      LOG_PRINT_KEY T
      FORMAT xyz
      UNIT angstrom
      &EACH
        GEO_OPT 1
      &END EACH
      ADD_LAST NUMERIC
    &END TRAJECTORY
  &END PRINT
&END MOTION

&FORCE_EVAL
  METHOD Quickstep
  &DFT
    BASIS_SET_FILE_NAME /usr/local/CP2K/BASIS_MOLOPT
    POTENTIAL_FILE_NAME /usr/local/CP2K/GTH_POTENTIALS
    &MGRID
      CUTOFF 100
    &END MGRID
    &QS
    &END QS
    &SCF
      SCF_GUESS ATOMIC
    &END SCF
    &XC
      &XC_FUNCTIONAL PBE
      &END XC_FUNCTIONAL
    &END XC
  &END DFT

  &SUBSYS
    &CELL
      A    15.0 0.0 0.00
      B    0.0 15.0 0.0
      C    0.0 0.0 15.0
      PERIODIC NONE
    &END CELL
    &COORD
      O         0.0006535865        0.0348037292        6.5225572751
      H        -0.0003839912       -0.0241840602        7.5017980482
      H        -0.0019131905        1.0517623171        6.4318839506
      O         0.0244126401        0.0102938023        4.0045222106
      H        -0.0164725514       -0.0290451673        5.4795600635
      H         1.0326311856        0.2923983937        4.3857121035
    &END COORD

    &KIND O
      BASIS_SET DZVP-MOLOPT-GTH-q6
      POTENTIAL GTH-PBE-q6
    &END KIND
    &KIND H
      BASIS_SET DZVP-MOLOPT-GTH-q1
      POTENTIAL GTH-PBE-q1
    &END KIND
  &END SUBSYS
&END FORCE_EVAL



-------------- next part --------------
An HTML attachment was scrubbed...
URL: <https://lists.cp2k.org/archives/cp2k-user/attachments/20140219/465139de/attachment.htm>