I'm studying a molecular crystal in which two different molecules form an 1:1 adduct. There are 2 molecules of each kind (4 in total) in the unit cell. There are 19 atoms in the asymmetric unit, and since it belongs to the P21/c spacegroup, a total of 76 atoms are contained in the unit cell. I was trying to find a possible mistake when calculating interaction energies and I found the next problem: If I calculate the SCF by manually inserting the 76 positions and giving it a P1 symmetry the energy converged to-5752.17735109 Ry. If I calculate the SCF by inserting the 19 atoms of the asymmetric unit with the correct symmetry and let the program to generate the rest of the positions (which where exactly the same as when inserted manually), the same functional, same RMT, same K points and same convergence criteria the energy converged to-5752.17735109 Ry. Transforming the energy difference between the 2 calculations gives 195 kcal/mol. The same happened when doing the same for other systems. My question is, ¿shouldn't I get the same energy in both calculations since it's the same system, same coordinates and the input was prepared equally except for the symmetry? Since I'm trying to calculate interaction energies using different subsystems, some with and some without symmetry, this is a relevant question to my research.
Greetings, Bruno L
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