Error : The optimization of the polarization energy failed

[Dipankar Saha]

Traceback (most recent call last):
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File "zipdir/NL/CommonConcepts/Configurations/AtomicConfiguration.py", line 1766, in update
File "build/lib/python2.7/site-packages/tremolox/TremoloBaseCalculator.py", line 431, in _update
tremolox.RuntimeError: Error in ../../../../src/madden.c line 4094: The optimization of the polarization energy failed, nlopt status: -1

What does it mean?

Best_
Dipankar

[Julian Schneider]

The potential you selected uses a polarization energy term in which the dipole moments on each atom needs to be computed self-consistently via optimization at each MD step
(see e.g. https://docs.quantumwise.com/manual/Types/MaddenParticle/MaddenParticle.html#maddenparticle-c or https://aip.scitation.org/doi/10.1063/1.1513312 ).

In your case the optimization of the dipoles did not meet the convergence criteria, which results in this error message.
Without knowing what system you are looking at I can only speculate that this could be due to that you have an unstable system which is tricky to optimize (i.e. atoms too close,) or not suited for this type of potential.
You could try to pre-optimize it with a simpler potential or use a simpler potential alltogether (if available).

An advanced possibility would be to change the optimization options in the Madden potential by adding a MaddenOptimizationOption to the potential set (see example in https://docs.quantumwise.com/manual/Types/MaddenOptimizationOption/MaddenOptimizationOption.html#maddenoptimizationoption-c
Here the parameters to play around with would be to increase the polMaxIterations (i.e. the max number of optimization iterations, default 200), or to increase the polFTol or polGradTol values (tolerance to stop the optimization, default values 10**-10 and 10**-4)

[Dipankar Saha]

Okay... / I will send you the script.
Thank you Julian for all the details ! 

Best_
Dipankar

[Ulrik G. Vej-Hansen]

Which method to calculate the MEP are you referring to?