[Wien] A question regarding a calculation for a 56 atoms unit cell

[Peter Blaha]

Are you using a recent version with MSEC1 in case.inm or an older one ?

As was mentioned several times gefore: changing the mixing parameter will most likely
NOT help with the new methods.

Using TEMP instead of TETRA may help convergence (but a too large value is dangerous).

Do you have a metallic or insulating state (I understand it SHOULD be an insulator, but do
you get it ?)

How many iterations did you run ? Sometimes (but not very often) more than 40 are required ..

Timing is strange. 56 atoms is not that big and it should not take a week ...
(? 2-fold k-point parallelization ?; OMP_NUM_THREAD =2??? to utilize all 4 cores ??)

I guess nobody can answer if your convergence is sufficient or not. It depends on the prupose
of your calculation. You need to monitor other
quantities like MMT or MMIxxx, FER, forces, :GAP,....

Am 05.06.2011 22:17, schrieb shamik chakrabarti:
> Dear wien2k users,
>
>                         We are running a SCF calculation for a *56 inequivalent atoms* unit cell. We have included spin polarization and self interaction correction (GGA+U) in
> this calculation. The calculation has been run for one week now without any errors. We are using a system having *Intel Xeon quad core processor and 8GB RAM*. We are using *14 K
> points* and a *mixing factor 0.1*. The energy and charge convergence were achieved up to *0.04*. Once energy convergence has also gone up to 0.008 but then again a bit diverges to
> come up to 0.04. Now my question is::
>
> (1)  Is it possible to achieve charge and energy convergence up to 0.0001 with this unit cell using the above mentioned system if we consider that all the interactions applied for
> this
>       material is proper?
> (2) If it is achievable then can we estimate how much time it can take given the no. of inequivalent atoms, K points, mixing parameter and nature of the processor?
> (3) If we are not able to achieve that much of convergence (0.0001) even after a long time (say 2 weeks) then is it right to stop the calculation if we achieve a stability in
> convergence
>      and say it is up to 0.01?
> (4) If we take the convergence up to 0.01 then how much reliable will be the further calculation of its properties (DOS) given the no. of K points is 14?
>
> (5) If we do not get the convergence say at least up to 0.01 is it right to increase the mixing parameter to say 0.15 or 0.20 given the system is a *localized magnetic system*?
>
> The system is an insulator and also contain Fe. Thats why we have also consider self interaction correction (GGA+U).
>
> Please forgive us for such a long email. We have to right it in this way as the calculation has already been taken a long time and are indicating to take longer time still.
> Any reply in this regard will be very helpful for us. Thanks in advance.
>
> with best regards,
>
> --
> Shamik Chakrabarti
> Research Scholar
> Dept. of Physics & Meteorology
> Material Processing & Solid State Ionics Lab
> IIT Kharagpur
> Kharagpur 721302
> INDIA
>
>
>
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-- 

                                       P.Blaha
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Peter BLAHA, Inst.f. Materials Chemistry, TU Vienna, A-1060 Vienna
Phone: +43-1-58801-15671             FAX: +43-1-58801-15698
Email: blaha at theochem.tuwien.ac.at    WWW: http://info.tuwien.ac.at/theochem/
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