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

[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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