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QuantumATK => General Questions and Answers => Topic started by: Dipankar Saha on July 10, 2017, 12:34

Title: Stress Error
Post by: Dipankar Saha on July 10, 2017, 12:34

Hi,

While using 2016.4 version, I find that the Optimizer_log reports "Stress Error (GPa)" .
How is this related with the stress tolerance ??

Best_
Dipankar

Title: Re: Stress Error
Post by: Julian Schneider on July 10, 2017, 12:49

The stress error tells you by how much the current stress deviates from the given target stress. The stress error must be below the given stress tolerance to consider the stress optimization converged.

Title: Re: Stress Error
Post by: Dipankar Saha on July 12, 2017, 12:25

Thanks Julian .../ But,  even if  there is no given "stress tolerance" (target), I find that  the "stress error" calculation is getting conducted!!! /  Is this now coupled with other constraints ??   

Title: Re: Stress Error
Post by: Julian Schneider on July 12, 2017, 13:58

If you use the ScriptGenerator:
You will only do a stress optimization if you uncheck the "Constrain Lattice Vectors" box, no matter what stress error tolerance value you give.

If you set up the calculation in a script:
Whether you do a stress optimization or not, depends on if you set the parameter

Code

disable_stress

to True (no stress optimization) or False (so a stress optimization).
If you don't set this keyword, the default is False, that means by default you do a stress optimization (see http://docs.quantumwise.com/manuals/Types/OptimizeGeometry/OptimizeGeometry.html#optimizegeometry-f (http://docs.quantumwise.com/manuals/Types/OptimizeGeometry/OptimizeGeometry.html#optimizegeometry-f)).
That also means you will perform a stress optimization, even if you don't explicitly give the stress error tolerance (i.e. via the

Code

max_stress

keyword). In that case the default stress tolerance of 0.1*GPa will be used.
Same with the

Code

target_stress

, here the default is 0.0*GPa, unless you specify something else.