[Wien] how to increase precision of calculations?
Peter Blaha
pblaha at theochem.tuwien.ac.at
Tue Dec 2 12:03:06 CET 2014
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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--
P.Blaha
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Peter BLAHA, Inst.f. Materials Chemistry, TU Vienna, A-1060 Vienna
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Email: blaha at theochem.tuwien.ac.at WIEN2k: http://www.wien2k.at
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