Geometry Optimization

[anup]

Dear Experts,

Greetings

I am having some problem to optimize the geometry of compound materials ABX3. What should be the limiting value of Force and Stress tolerance ? Also, I have a confusion that, after optimizing the geometry, will the new position of  atoms also have almost identical structure to their parent structure ? or the new structure will be completely distorted ?

[Petr Khomyakov]

You may want having a look at this tutorial https://docs.quantumwise.com/tutorials/geometry_optimization/geometry_optimization.html.

The choice for Force and Stress tolerance is totally up to you, as it depends how close you want your structure to be to equilibrium.  However, you have to keep in mind that using strict convergence for forces and stress assumes that the total energy tolerance parameter is also small enough, since Forces and Stress are calculated from the total energy.

Regarding the atomic motion during the optimization process, it really depends how far your system is from equilibrium. In principle,  in some cases you may observe significant structural modifications. So, it is totally problem specific.