[Wien] Charge Convergence is not achieved

[Shamik Chakrabarti]

Dear Peter Blaha Sir,

                       Indeed by increasing number of K points we got the
convergence. Sir I have now some basic queries on this topic. You have said
that
                    "sometimes you cannot reach (easily) arbitrary
convergence"
why in some cases we can not reach convergence up to our desired limit?...is
it the limitation of DFT?....or it means that the feasibility of the
solution is only up to the achieved convergence?

Thanking you,
with best regards,

On Wed, Jul 6, 2011 at 6:13 PM, Peter Blaha <pblaha at theochem.tuwien.ac.at>wrote:

> For just 3 atoms/cell (and metallid ??) 1000 or 5000 k are still not much.
> Better k-mesh should improve convergence.
>
> And sometimes you cannot reach (easily) arbitrary convergence. What about
> E-tot, ... ?
>
>
> Am 06.07.2011 07:48, schrieb Shamik Chakrabarti:
>
>> Dear wien2k users,
>>
>> We have done volume optimization of a structure having space group no. 225
>> (Fm3m) and 3 inequivalent atoms per unit cell. We have taken the least
>> energy lattice parameters for
>> spin polarized SCF calculations. However, the last calculation (spin
>> polarized SCF) has not been converging at all. We have set the convergence
>> criteria of  charge to 0.0001and it
>> reached up to 0.006. After that its is fluctuating sinusoidally at this
>> value (even at around 400th iteration). We have also tried using the
>> fallowing steps, such as
>>
>> 1. increasing the RmaxKmax value from 7 to 9
>>
>> 2. changing mixer values ranging from 0.01 to 0.3 (using MSEC mixing
>> scheme...wien2k 10)
>>
>> 3. increasing the K-points from 1000 to 5000
>>
>> but unfortunately we haven't got the desired convergence yet. Therefore,
>> it is very helpful for us to have a suggestion for this problem.
>>
>> --
>> 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
> ------------------------------**------------------------------**
> --------------
> 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/ <http://info.tuwien.ac.at/theochem/>
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-- 
Shamik Chakrabarti
Research Scholar
Dept. of Physics & Meteorology
Material Processing & Solid State Ionics Lab
IIT Kharagpur
Kharagpur 721302
INDIA
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