ABINIT Discussion Forums

hello every body,
I have a compound optimized in three different space groups (one is primitive tetragonal and two are centered). I obtain nearly the same cell parameters, the same energy and the atoms of the the three structures seems to relax toward the same positions while keeping some distorsions that keeps abinit declaring the three structures different. However, if I "relax" tolsym to 5d-4 for one structure and 2d-3 for the second the symmetry finder gives the same space group as the third one.
my question is : may I consider that actually I have the same structure (with the same space group) and that the diffrences are negligible.
thank you for your comments.

It sounds like the differences are negligible, but you might be looking for something more subtle (another property which is still not identical between the different structures). This depends on your goal here.

Similarly, there is no general rule for how converged you need to be to declare there is no difference in the structures - "converged enough". Good numerical precision is meV per atom, but again that depends on the system.

Matthieu

Hi Matthieu,
thank you for replying,
I did not notice your reply until today.

It sounds like the differences are negligible, but you might be looking for something more subtle (another property which is still not identical between the different structures). This depends on your goal here.

I am just looking for total energy differences.

Similarly, there is no general rule for how converged you need to be to declare there is no difference in the structures - "converged enough". Good numerical precision is meV per atom,

only my differences are converged to 1 meV, so I would consider that within this numerial accuracy the three structures are the same.

thank you.