Error in Geometry Optimization of nanosheet

[Subhban15]

1. The following error flashes whenever I try to optimize the geometry of any nanosheet with Slater Koster. Could anyone please explain what it means?

Traceback (most recent call last):
  File "/tmp/9271670433236302.py", line 97, in <module>
    optimizer_method=LBFGS(),
  File "./zipdir/NL/Dynamics/Optimization/OptimizeGeometry.py", line 232, in OptimizeGeometry
  File "./zipdir/NL/Dynamics/Optimization/OptimizeGeometry.py", line 287, in runRelaxation
  File "./zipdir/NL/Dynamics/ASEAtomsInterface.py", line 264, in get_forces
  File "./zipdir/NL/Dynamics/ASEAtomsInterface.py", line 159, in _update
  File "./zipdir/NL/Analysis/Forces.py", line 29, in __init__
  File "./zipdir/NL/Calculators/HuckelCalculator/Analysis/Forces.py", line 23, in calculateHuckelForces
  File "./zipdir/NL/Calculators/HuckelCalculator/Analysis/EnergyForcesStressUtilities.py", line 168, in setupEnergyForcesStress
NL.ComputerScienceUtilities.Exceptions.NLValueError: No PairPotential given, which is required in order to calculate forces or stress.

2. Why can we not optimize the geometry using Extended Huckel? Is it a software problem or a practical one?

Thanks in advance!

[Anders Blom]

No, you cannot optimize a structure using Huckel, the model doesn't support the evaluation of forces on the atoms properly.

[Subhban15]

Okay, thank you!

But what about Slater Koster, what does the error mean?

[Anders Blom]

Same

[Subhban15]

While using Huckel the OptimizeGeometry option gets disabled, whereas with Slater Koster the error is showed after the simulation begins.
Moreover, on rechecking I found that with carbon nanosheet ATK is showing the same error, whereas with Si nanosheet the error persists.
I would be grateful if you explain the same. Thanks!

[Anders Blom]

Didn't understand the above, but generally Huckel and SK do not work for geometry optimization. DFTB does, but the parameter sets shipped with ATK are not good (they are just demos) - you should get parameters from dftb.org instead. Or use DFT :-) Or a classical potential, there are many decent carbon potentials.

[Subhban15]

My bad, I wrote it wrong, sorry...

*Moreover, on rechecking I found that with carbon nanosheet the simulation takes place and generates an optimized sheet (may not be accurate though) whereas with Silicene nanosheet (which is of my concern) the error message flashes.*

Thank you for the site that you have mentioned. I will go through it.

Actually, optimizing through DFT is taking a lot of time and so I was trying the other methods.

Thanks again!