[CP2K-user] [CP2K:11324] Weird "convergence" of L-BFGS CELL_OPT

hut... at chem.uzh.ch hut... at chem.uzh.ch
Fri Feb 22 14:03:31 UTC 2019


without SCF convergence, all geometry/cell optimizers will behave
strange. Make sure that you wavefunctions converge!

In a workflow calculation I would start with a single point SCF
calculation and ensure convergence. Starting from a converged
WFN is usually rather save.

If your system has a gap, I would use OT with CG and Linesearch
for the initial WFN optimization.
For special spin states setting a magnetic moment in the kind section
could help.


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: "Daniele Ongari" 
Sent by: cp... at googlegroups.com
Date: 02/22/2019 02:39PM
Subject: [CP2K:11324] Weird "convergence" of L-BFGS CELL_OPT

Dear CP2K mailing list,

We experience a strange behavior of the L-BFGS optimization algorithm when dealing with cases where SCF convergence is problematic.

After 20 minimization steps the cp2k printed the following:

--------  Informations at step =    21 ------------
 Optimization Method        =                LBFGS
 Total Energy               =     -2345.6430825804
 Internal Pressure [bar]    =        23.9760390703
 Real energy change         =         0.0028283710
 Decrease in energy         =                   NO
 Used time                  =             5864.105

 Convergence check :
 Max. step size             =         0.0000000000
 Conv. limit for step size  =         0.0030000000
 Convergence in step size   =                  YES
 RMS step size              =         0.0000000000
 Conv. limit for RMS step   =         0.0015000000
 Convergence in RMS step    =                  YES
 Max. gradient              =         0.0082916384
 Conv. limit for gradients  =         0.0004500000
 Conv. for gradients        =                   NO
 RMS gradient               =         0.0009846623
 Conv. limit for RMS grad.  =         0.0003000000
 Conv. for gradients        =                   NO
 Pressure Deviation [bar]   =       -76.0239609297
 Pressure Tolerance [bar]   =       100.0000000000
 Conv. for  PRESSURE        =                  YES


* Specific L-BFGS convergence criteria
* satisfied .... run CONVERGED!

The two things that look strange for us are:

1) Max. step size and RMS step size were 'artificially' set to 0.0000000000
2) Not all checks are showing convergence, while L-BFGS algorithm has decided to stop.

Therefore, we would like to know if this is an expected behavior of the L-BFGS algorithm and if yes, what is the reason behind working this way?

Please see input and output files attached.

With best regards,
Daniele and Sasha  
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