[CP2K-user] CELL Optimization - Energy not decreasing

[Jan Elsner]

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


-------------- next part --------------
An HTML attachment was scrubbed...
URL: <https://lists.cp2k.org/archives/cp2k-user/attachments/20200418/af8a2385/attachment.htm>
-------------- next part --------------
A non-text attachment was scrubbed...
Name: cell.inp
Type: chemical/x-gamess-input
Size: 2529 bytes
Desc: not available
URL: <https://lists.cp2k.org/archives/cp2k-user/attachments/20200418/af8a2385/attachment.inp>
-------------- next part --------------
A non-text attachment was scrubbed...
Name: cell.out
Type: application/octet-stream
Size: 2912444 bytes
Desc: not available
URL: <https://lists.cp2k.org/archives/cp2k-user/attachments/20200418/af8a2385/attachment.obj>
-------------- next part --------------
A non-text attachment was scrubbed...
Name: E_vs_cutoff.png
Type: image/png
Size: 92373 bytes
Desc: not available
URL: <https://lists.cp2k.org/archives/cp2k-user/attachments/20200418/af8a2385/attachment.png>
-------------- next part --------------
A non-text attachment was scrubbed...
Name: subsys.include
Type: application/octet-stream
Size: 1973 bytes
Desc: not available
URL: <https://lists.cp2k.org/archives/cp2k-user/attachments/20200418/af8a2385/attachment-0001.obj>