Supercell energies

[ams_nanolab]

I have a basic question, I have two large supercells (same materials, slightly different configuration) showing total energies -97430.8445 and -97430.8925 eV. What does such a large value physically mean?  And from this what can I gather about the stability of the two systems?

[Anders Blom]

Large value = many atoms. The total energy per atom is a more relevant number.
From the numbers themselves you can learn nothing. They have to be put in a context, for instance the total energy change when you modify the system.

[ams_nanolab]

Okay , the no. of atoms are same for two cells just some rearrangement (rotation) has been done. -97430.8445 is at an angle theta_1 and -97430.8925 eV is at an angle theta_2. So the second case should be more stable (more negative energy), correct? In such i don't need energy/atom?

[Anders Blom]

No you don't need to normalize. "Stable" is perhaps not the exactly correct word, as stability also has to do with the phonon spectrum etc. But if the structure itself is stable, the the version with lower energy is more favorable.