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General Questions and Answers / About stress tolerance in v11.2
« on: March 18, 2011, 22:10 »
Hi,
I am using the latest version of ATK and found that the optimizeGeometry() method allows relaxation of a bulk material to extract its optimal lattice constant, according to the stress that is "felt" by the unit cell. A stress tolerance value is required (maximum_stress) for the method to determine when the relaxation stops. I am wondering if someone could give me suggestions on how to set this stress tolerance.
The default value given by the Script Generator is maximum_stress=0.05eV/Ang**3, which is approximately 8.01 GPa. This value seems orders of magnitude larger than the stress usually found in a metal. As an example, the yield strength of Ni is 14-35MPa, according to http://en.wikipedia.org/wiki/Yield_(engineering). When I tried to relax bulk Ni with a maximum_stress=1e-4eV/Ang**3 (16MPa), it took a long time and the lattice constant became 14.81Ang, while the experimental lattice constant is about 3.52Ang.
I used SGGA+U for exchange-correlation, but set all the Hubbard U terms to zero.
Thanks!
I am using the latest version of ATK and found that the optimizeGeometry() method allows relaxation of a bulk material to extract its optimal lattice constant, according to the stress that is "felt" by the unit cell. A stress tolerance value is required (maximum_stress) for the method to determine when the relaxation stops. I am wondering if someone could give me suggestions on how to set this stress tolerance.
The default value given by the Script Generator is maximum_stress=0.05eV/Ang**3, which is approximately 8.01 GPa. This value seems orders of magnitude larger than the stress usually found in a metal. As an example, the yield strength of Ni is 14-35MPa, according to http://en.wikipedia.org/wiki/Yield_(engineering). When I tried to relax bulk Ni with a maximum_stress=1e-4eV/Ang**3 (16MPa), it took a long time and the lattice constant became 14.81Ang, while the experimental lattice constant is about 3.52Ang.
I used SGGA+U for exchange-correlation, but set all the Hubbard U terms to zero.
Thanks!