[Wien] SCF and symmetry

[Peter Blaha]

No. This is a huge E-difference which must come from something very 
severe. Did you compare the distances in the 2 case.outputnn file or 
compare the structures in xcrysden.

On 12/01/2015 07:37 AM, Bruno Landeros wrote:
> 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 <mailto: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
> <mailto: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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> --
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-- 

                                       P.Blaha
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Peter BLAHA, Inst.f. Materials Chemistry, TU Vienna, A-1060 Vienna
Phone: +43-1-58801-165300             FAX: +43-1-58801-165982
Email: blaha at theochem.tuwien.ac.at    WIEN2k: http://www.wien2k.at
WWW:   http://www.imc.tuwien.ac.at/staff/tc_group_e.php
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