[CP2K-user] [CP2K:13145] CELL Optimization - Energy not decreasing

[hut... at chem.uzh.ch]

Hi

I don't know how well a setup as this is tested. However, from
your output I would guess the problem could be related to your
SCF convergence. With the methods you are using you have to set
the convergence criteria much tighter in order to get converged
energy and forces. I would suggest to use at least 1.E-8.

The ultimate test would be to do a DEBUG run in order to verify
forces and stress tensor for the setting of options.

regards

Juerg Hutter
--------------------------------------------------------------
Juerg Hutter                         Phone : ++41 44 635 4491
Institut für Chemie C                FAX   : ++41 44 635 6838
Universität Zürich                   E-mail: hut... at chem.uzh.ch
Winterthurerstrasse 190
CH-8057 Zürich, Switzerland
---------------------------------------------------------------

-----cp... at googlegroups.com wrote: -----
To: "cp2k" <cp... at googlegroups.com>
From: "Jan Elsner" 
Sent by: cp... at googlegroups.com
Date: 04/18/2020 08:33PM
Subject: [CP2K:13145] CELL Optimization - Energy not decreasing

Dear all, 

I am trying to run a Cell Optimisation on a periodic molecular crystal (beta-resorcinol: C6H6O2, 4 molecules in unit cell) using K-points and BFGS as optimiser. I am using the vdW-DF-optPBE functional (https://github.com/cp2k/cp2k/commit/74ef05b96a46523a0daf7da04e75804420b5cd5e). After 83 optimisation steps, my system does converge to the required MOTION thresholds, however from step 7 onwards the total energy increases at every step i.e.:

--------  Informations at step =     7 ------------
  Optimization Method        =                 BFGS
  Total Energy               =      -280.1489665596
  Internal Pressure [bar]    =     -2667.4573178334
  Real energy change         =         0.0001037473
  Predicted change in energy =        -0.0001063956
  Scaling factor             =         0.0000000000
  Step size                  =         0.0124910496
  Trust radius               =         0.4724315332
  Decrease in energy         =                   NO
  Used time                  =               60.978

  Convergence check :
  Max. step size             =         0.0124910496
  Conv. limit for step size  =         0.0010000000
  Convergence in step size   =                   NO
  RMS step size              =         0.0029192108
  Conv. limit for RMS step   =         0.0010000000
  Convergence in RMS step    =                   NO
  Max. gradient              =         0.0034738629
  Conv. limit for gradients  =         0.0001000000
  Conv. for gradients        =                   NO
  RMS gradient               =         0.0006857738
  Conv. limit for RMS grad.  =         0.0001000000
  Conv. for gradients        =                   NO
  Pressure Deviation [bar]   =     -2668.4705678334
  Pressure Tolerance [bar]   =       200.0000000000
  Conv. for  PRESSURE        =                   NO
 ---------------------------------------------------

The resulting cell-optimised structure is therefore not a minimum in energy. I've attached the input and output files. Some points which may (or may not) be relevant:
I did not encounter this problem when using a different functional (PBE + D3 instead of optPBE-vdW as used here), but otherwise identical settings.
I encountered the same issue (energy increasing at every step) using CUTOFF/REL_CUTOFF = 800/60
I initially tried to converge CUTOFF and REL_CUTOFF as in the tutorial (
https://www.cp2k.org/howto:converging_cutoff), however my single point calculations did not converge quite as nicely as in the tutorial - instead oscillating with an amplitude of order ~ e-4 Ha (I've attached a figure showing this). This is why I use such large CUTOFF/REL_CUTOFF values. I note that this was also the case when I ran PBE + D3 calculations, however in the latter case my cell optimisation did work. 

Any input would be greatly appreciated. 

Best wishes, 

Jan


  
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[attachment "cell.inp" removed by Jürg Hutter/at/UZH]
[attachment "cell.out" removed by Jürg Hutter/at/UZH]
[attachment "E_vs_cutoff.png" removed by Jürg Hutter/at/UZH]
[attachment "subsys.include" removed by Jürg Hutter/at/UZH]