Calculation of stability SnS

[AD]

Hello all,

I am a new user in the quantumwise community, so please accept my greetings.

Starting with the main business, I would like to ask how I can evaluate the stability of
materials using quantumwise? I have two structures taken from materialsproject website
for SnS bulk (62 pnmahttps://materialsproject.org/materials/mp-2231/
and
63 cmcmhttps://materialsproject.org/materials/mp-559676/ group). I see on the website that the
62 structure (alpha phase) is more stable if we look at the energies per atom.
I wanted to obtain the same conclusion using GGA functionals, but I always find that beta is slightly
more stable than alpha. I did Geometry optimization using high kpoints (9x9x9 and 13x13x13)
with PBE and PBES. Even though the energy difference is smaller on the website as well, it does
mention that 63 decomposes to 62. I also use DFTD2 corrections. Can someone point out why
this could be happening?

Additional note: I left the simulations to compelte overnight. Next day the logs still show that
                        some part of the calculations are still being evaluated while the jobmanager show
                        that they are done. Using version 2014.1. While this has nothing to do with the results
                        as even if logs are ok, the calculations are still the same.

Thanks in advance for your suggestions.

[Ulrik G. Vej-Hansen]

The energy difference between the two phases is quite small, so it will not be all combinations of pseudopotentials and basis sets which can capture it. You do not state which you have used, but I would suggest trying the different SG15 basis sets, including Ultra, and using rather high mesh cutoffs, say, 200 Hartree.

I do not understand exactly what you mean about the Job Manager, could you provide a more detailed explanation? By the way, you should be using version 2014.3, which contains bug-fixes and other improvements compared to 2014.1.

[AD]

Thanks Ulrik for your reply. Indeed the difference is too small. I am using GGA-PBE with double zeta polarized basis. I will try as suggested. By job manager I meant the window where we see all the queued or running jobs. There I saw that the job status is done but when I clicked the log option just beside it, I found that the job was not finished. No calculations were in progress though. Maybe the log was not written anymore. Anyway, it's not a recurring problem and happened only once. Thanks for your suggestion.

[AD]

I tried increasing the cutoff to 200 Hartree and also changed the limits for force and stress tolerances to 0.001 and 0.0001 respectively.
Everything else remains the same (2015 version as I don't have 2016) GGA -PBE, DFT-D3. The 62 structure alpha phase converges while 63 runs into an error pasted below:

Traceback (most recent call last):
  File "SnS_63_orig.py", line 76, in <module>
    optimizer_method=LBFGS(),
  File "./zipdir/NL/Dynamics/Optimization/OptimizeGeometry.py", line 331, in OptimizeGeometry
  File "./zipdir/NL/Dynamics/Optimization/OptimizeGeometry.py", line 497, in runSimultaneousRelaxation
  File "./zipdir/NL/Dynamics/Optimization/OptimizeGeometry.py", line 401, in runRelaxation
  File "./zipdir/NL/Dynamics/Optimization/OptimizerMethod.py", line 502, in step
  File "./zipdir/NL/Dynamics/StrainFilter.py", line 133, in set_positions
  File "./zipdir/NL/Dynamics/ASEAtomsInterface.py", line 243, in _updateCell
  File "./zipdir/NL/CommonConcepts/Configurations/ConfigurationCopy.py", line 145, in stretchRelaxationCell
  File "./zipdir/NL/CommonConcepts/Configurations/ConfigurationCopy.py", line 113, in newLatticeFromCell
  File "./zipdir/NL/CommonConcepts/Configurations/BravaisLattice.py", line 1970, in __init__
  File "./zipdir/NL/CommonConcepts/Configurations/BravaisLattice.py", line 1311, in __init__
  File "./zipdir/NL/CommonConcepts/Configurations/BravaisLattice.py", line 194, in checkValidLength
NL.ComputerScienceUtilities.Exceptions.NLValueError: The lattice parameter a must be larger than 0*Units.Ang


What could possibly lead to 0*Units.Ang ?

Thanks

[Ulrik G. Vej-Hansen]

Good question - could you please attach the exact .py and .log files from this calculation? Than I can look into it.