Typos in your energies?

On Mon, Nov 30, 2015 at 8:00 PM, Bruno Landeros <brunolande...@hotmail.com>
wrote:

> 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
>



-- 
Professor Laurence Marks
Department of Materials Science and Engineering
Northwestern University
www.numis.northwestern.edu
Corrosion in 4D: MURI4D.numis.northwestern.edu
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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