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

[Krack Matthias (PSI)]

Hi Daniele

The SCF runs did not converge in the CP2K output file which you attached. Thus, you are feeding the L-BFGS optimiser with invalid atomic forces.
Though the L-BFGS might get stuck in that way even with valid forces, this can usually be overcome by a restart or by using BFGS if possible.

Matthias

From: cp... at googlegroups.com <cp... at googlegroups.com> On Behalf Of Daniele Ongari
Sent: Freitag, 22. Februar 2019 14:39
To: cp2k <cp... at googlegroups.com>
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
---------------------------------------------------

--------------------------
OPTIMIZATION STEP:     22
--------------------------

***********************************************
* Specific L-BFGS convergence criteria
* WANTED_PROJ_GRADIENT and WANTED_REL_F_ERROR
* 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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