[Wien] how to increase precision of calculations?
Martin Gmitra
martin.gmitra at gmail.com
Wed Dec 3 12:04:37 CET 2014
Dear Peter,
Thank you for your effort. I have modified lapwso and lapw1 so that
1/3 and 2/3 are entered in machine precision. The non-continuous
behavior stays the same even with your suggestions for RKmax=10,
Emax=9999.9 and adding RLOs in case.inso (could you comment please why
consider RLOs in the GaAs case?). I had also changed the non-primitive
translations exactly to 0 (did not mentioned last time) with no
effect.
I am observing that splitting goes perfectly smooth along the Gamma-H
line. Therefore I plotted splitting along "Gamma-K" direction with a
tiny kz component. Please see attached plots (idv=36000) for kz=0;
kz=1/36000 and kz=5/36000. The smoothness gets slowly recovered. Could
it be a helpful information to extract a reason for the problem?
Best regards,
Martin
On Tue, Dec 2, 2014 at 12:03 PM, Peter Blaha
<pblaha at theochem.tuwien.ac.at> wrote:
> Hi,
>
> I could confirm the problem, but unfortunately I cannot offer a solution.
>
> These irregulations do not go away with increasing RKMAX or Emax (best is
> anyway to set EMAX=9999.9 in case.in1 for such a study).
> Changing compiler options (higher precision of ifort) or even changing to
> gfortran or older WIEN2k versions does not cure the problem.
>
> They come from eigenvalue differences in the 9th digit after the comma.
>
> If I check internal accuracy, for instance by calculations for all 6
> equivalent k-points (x,x,0;-x,-x,0;2x,-x,0,....) such differences should
> still be feasible, because internal consistency is 11 digits in lapwso (but
> 14 in lapw1, so clearly we are loosing something there), see below.
> 58 0.449061656042513
> 58 0.449061656068273
> 58 0.449061656046884
> 58 0.449061656046190
> 58 0.449061656032196
> 58 0.449061656067333
> *
>
> In any case, for an accurate value of your quantity (delta-E/k) you need at
> least
>
> RKMAX=10
> Emax=9999.9 (all eigenvalues in lapw1)
> add RLOs for both atoms in case.inso !!
>
> and then have to extrapolate from the smooth part of the curve.
>
> Change the non-primitive translation in case.struct to be exactly 0 !
>
> PS: another sophisticated test would be to convert your structure to an
> orthorhombic one and test if the problem comes from the hexagonal lattice
> (positions like 1/3, ... are never "correct" in the input), although then
> you might have a problem to specify your k-points with full accuracy; or at
> least modify lapw1/lapwso and set the input 0.3333333 to 1/3 internally ..
>
>
>
> On 12/02/2014 08:22 AM, Martin Gmitra wrote:
>>
>> Dear Stefaan,
>>
>> Yes, I have increased the Emax parameter to 18 Ry, see blue curve in
>> right plot. Indeed, it is one of the most important parameters.
>>
>> Best,
>> Martin
>>
>>
>> On Mon, Dec 1, 2014 at 1:20 PM, Stefaan Cottenier
>> <Stefaan.Cottenier at ugent.be> wrote:
>>>
>>>
>>>> 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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>>>>>
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>
> --
>
> P.Blaha
> --------------------------------------------------------------------------
> 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
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