# Unusual behavior of CI-NEB calculation

Tobias Kraemer 161brun... at gmail.com
Fri Oct 9 12:41:05 CEST 2015

```Hi all,

I am observing some strange behavior during a NEB calculation. Basically,
the job has been running for a long time, but didn't seem to get close to
converging. Checking the output it turns out that following step 20 (so
right at the beginning)
there weren't any convergence checks any more. Hence, this is the last
convergence check I get:

*******************************************************************************
BAND TYPE                     =
CI-NEB
BAND TYPE OPTIMIZATION        =
SD
STEP NUMBER                   =
20
NUMBER OF NEB REPLICA         =
16
DISTANCES REP =        0.904376        0.970665        1.003149
0.989286
0.919178        0.879384        0.898267
0.929957
0.917761        0.958179        0.913835
0.867431
0.835008        0.833033        0.824020
ENERGIES [au] =    -4477.534580    -4477.534142    -4477.532777
-4477.530610
-4477.527827    -4477.524573    -4477.520887
-4477.517698
-4477.523689    -4477.538783    -4477.543540
-4477.546473
-4477.548883    -4477.550356    -4477.551290
-4477.540294
BAND TOTAL ENERGY [au]        =
-71640.56568602792686
*******************************************************************************
*******************************************************************************
RMS DISPLACEMENT =   0.00015     [ 0.00010]
( NO)
MAX DISPLACEMENT =   0.00872     [ 0.00020]
( NO)
RMS FORCE        =   0.00014     [ 0.00030]
(YES)
MAX FORCE        =   0.00652     [ 0.00080]
( NO)
*******************************************************************************

NEB| Computing Energies and Forces
NEB| REPLICA Nr.    1- Energy and Forces
NEB|                                     Total Energy:
-4477.534579955
NEB|    ATOM                            X                Y                Z
NEB|      Rh                      0.000001025     -0.000015044
0.000003010
NEB|      P                      -0.000001915      0.000000815
-0.000002622
NEB|      C                      -0.000000579      0.000005799
0.000000635
NEB|      C                      -0.000003518     -0.000003207
-0.000002095

What follows are Energies and Forces for the rest of the file. I can't find
any problems with SCF convergence in the BAND files, the energy profile
looks perfectly sensible, the trajectory of the last 16 images also makes
total sense to me. I find it hard to believe that this is a program bug,
since the very same input has successfully worked for a good number of
transition states in the meantime, on the very same system. However, it
strikes me that there appear no convergence reports after 20 steps. I also
noted that there isn't necessarily such a
convergence check after forces have been calculated for the 16 images I
have defined, so how does this work exactly? And why did I still get
sensible results for the other Transition States, while in the present
example the calculation seems to run into nowhere.

Tobias

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