[Wien] SCF and symmetry

[Bruno Landeros]

Dear Peter:




Yes, my mistake. First energy (no symmetry) is


-5752.55335845 Ry.

while second energy is

-5752.17735109 Ry.




Since cell parameters are note small (12.994513, 25.002400, 17.381701 Bohr)

and I was testing convergence I asked for just 1 K point in both cases. 

May be this the origin of the discrepancy?


Greetings,


Bruno






Enviado desde Correo de Windows





De: pblaha at theochem.tuwien.ac.at
Enviado el: ‎martes‎, ‎1‎ de ‎diciembre‎ de ‎2015 ‎12‎:‎16‎ ‎a. m.
Para: wien at zeus.theochem.tuwien.ac.at





The energies you posted are identical !

Anyway: I hope you did not just copy the case.klist file from the low to 
the high-symmetry case ??

Otherwise: send me your 2 struct files together with the description of 
the chosen calculational parameters (everything which is non-default) to 
my private email.

Am 01.12.2015 um 03:00 schrieb 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 research.
>
>
> Greetings,
>
> Bruno L
>
>
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