Forces and stress

[GJK]

Hi,

We optimize a system through functionalisation.How to calculate the average vale of forces and stress. We get the force and stress components in three dimensions.

Thank you

[zh]

The forces are exerted on every atom.  The stress is exerted on the cell lattice.    The average of stress is usually taken over the diagonal terms (i.e., sigma_11, sigma_22, sigma_33). This average of stress gives the pressure on the cell lattice.

After the geometry optimization, the forces on atoms and the stress on cell should converge to a threshold value (specified by the user in the geometry optimization).

"How to calculate the average vale of forces and stress."
So, your question is hard to be understood. 

[GJK]

In the analysis we have forces and stress to be calculated for an optimized system .How to get that average value I asked.

[Jess Wellendorff]

Here's how I would do it. Attached 2 scripts. As an example, Na2O2.py performs geometry optimization without minimizing the stress, and computes the Forces and Stress analysis objects. The script averages.py reads the analysis objects and computes averages in various ways.

Results:
<Force> : +1.120e-10 eV/Ang
<Stress>: -3.525e+00 GPa

Average force components:
<Fx>: +3.357e-10 eV/Ang
<Fy>: +4.524e-14 eV/Ang
<Fz>: +1.786e-13 eV/Ang