Dear Laurence Marks:

Yes, I'm sorry. First energy is:

-5752.55335845 Ry

Second energy is 

-5752.17735109 Ry

Enviado desde Correo de Windows

De: Laurence Marks
Enviado el: ‎lunes‎, ‎30‎ de ‎noviembre‎ de ‎2015 ‎09‎:‎06‎ ‎p. m.

Typos in your energies?

On Mon, Nov 30, 2015 at 8:00 PM, Bruno Landeros <> 

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 


Bruno L


Professor Laurence Marks
Department of Materials Science and Engineering
Northwestern University
Corrosion in 4D:
Co-Editor, Acta Cryst A
"Research is to see what everybody else has seen, and to think what nobody else 
has thought"
Albert Szent-Gyorgi
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