[Wien] how to increase precision of calculations?

[Stefaan Cottenier]

> Thanks for your reply and suggestions. I went with RKmax up to 12Ry
> and it turned out that 11 and 12 should be okay, since the splitting
> starts to "oscillate" (change in the increasing trend with increased
> RKmax). Concerning the non smooth behavior of the curve I did several
> test calculations playing around with the input parameters and none of
> the changes have brought desired healing of the step close to 0.003. I
> am attaching plots to the attachment.

 From your mail, it's not clear whether or not you tried to increase 
Emax, as Fabien suggested. This is specified in the last line of 
case.in1, and is different from RKmax which is at the top of that file. 
For spin-orbit effects, this is the most important precision-determining 
feature.

Stefaan


> On Sun, Nov 30, 2014 at 12:02 AM,  <tran at theochem.tuwien.ac.at> wrote:
 >>
>> Actually, the most important is maybe the number of bands calculated
>> by lapw1 which are used for the 2nd variational procedure for the
>> spin-orbit coupling. So, to increase Emax in case.in1 (up to 20 Ry or even
>> more) should be tried.
>>
>> F. Tran
>>
>>
>> On Sat, 29 Nov 2014, tran at theochem.tuwien.ac.at wrote:
>>
>>> Hi,
>>> For the convergence, I suggest to increase RKmax further. RKmax=8 is
>>> (very) good, but also not fully converged usually. Going up to
>>> RKmax=10 makes sense.
>>>
>>> It's difficult to say for the step at 0.003. Maybe the k-mesh is still
>>> not dense enough. An increase of GMAX (12 -> 18) in case.in2 is worth to
>>> try.
>>>
>>> F. Tran
>>>
>>> On Sat, 29 Nov 2014, Martin Gmitra wrote:
>>>
>>>> Dear Wien2k users,
>>>>
>>>> We are calculating spin-orbit coupling splitting of valence band in
>>>> wurtzite GaAs using mBJ. Since we are interested in a fine structure
>>>> close to Gamma point, we need to achieve sufficient accuracy. I am
>>>> attaching a plot of the valence band spin-orbit coupling splitting
>>>> (divided by the amplitude of k) as a function of k from the Gamma
>>>> point (k=0). As you can see, the splitting is sensitive to RKmax and
>>>> it does not look like it is going to "converge". What bothers me in
>>>> addition, is the step in the curves around 0.003 which can not be
>>>> healed by increasing RKmax (a smooth behavior as close as possible to
>>>> the Gamma point is desired result). I would like to add that
>>>> increasing k-mesh density does not affect the results as well as
>>>> increasing IFFT factor or reducing RMTs.
>>>>
>>>> Do you have any suggestions?
>>>> Best regards,
>>>> Martin Gmitra
>>>> Uni Regensburg
>>>>
>>>
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