[Wien] What RKmax and k-points I should take for the system LiGaTe2?
Peter Blaha
pblaha at theochem.tuwien.ac.at
Tue Feb 20 15:30:40 CET 2018
It was just mentioned 2 days ago on the mailing list: The total energy
:ENE is usually NOT a good criterion for a convergence test, as it is
most of the time NOT necessary to converge this number to mRy.
a) You have to consider your RMTs of Li, Ga and Te and calculate the
"effective RKMAX" for all 3 atoms. Suppose you have spheres of 2.0, 2.2
and 2.2 bohr, then RKMAX is effective for Li. But a RKMAX=4.5 for Li,
means an approximate RKMAX of 5 (10% larger) for Ga and Te. This is
certainly too small.
Also note, that the values in the Table are as mentioned there for
"low-medium quality" convergence only.
b) You have to monitor the quantity you want to publish.
For instance if your system has forces and you want to optimize the
internal positions (and publish them), monitor the forces. Do a "run
-min" calculation with RKmax=6 and 200k, save the results, increase eg.
RKmax to 7 and just do a "run -fc 1". Now compare the forces of the
saved RKmax=6 and the RKmax=7 calculation. If they do not differ by more
than a few mRy, you are probably done (unless you want highest precision
or expect soft modes (shallow potential landscape like in vdWaals
systems, ...)
If you want to publish a bandstructure, do the calculation with two sets
of parameters and compare the bandstructures, ......
Same for DOS, optic, magnetic moments, ....
You always have to make at least 2 calculations with different
parameters and convince yourself that the result you publish is (nearly)
constant.
Am 20.02.2018 um 09:00 schrieb Muhammad Shahzad Yasin:
> Respected Wien2k user,
>
> This is my first email to the mailing list.
> I am doing DFT calculations for LiGaTe2.
>
> As per FAQ of Wien2k for a system having Li, RKmax 4.5 is enough:
> http://susi.theochem.tuwien.ac .at/reg_user/faq/rkmax.html
> <http://susi.theochem.tuwien.ac.at/reg_user/faq/rkmax.html>
> I wanted to optimize this value and performed optimization for LiGaTe2.
> I used two different kpoints: 500 and 1000 in FBZ for RKMax optimization
> and RKmax=7 for k-point optimization.
>
>
> I am worried as the optimized value of RKmax obtained 9-10.5 and RKmax
> k-point optimization curve is not properly conversed and both the
> optimization parameters, RKmax and k-points are certainly too high.
>
>
>
> Below are my optimized parameters:
>
>
> 1. At k-points 500:
>
> ***********************
> ============================
> rkmax: | Etotal:
> ===========|================
>
> 4.5 -62173.36830033
> 5.0 -62173.71216556
> 5.5 -62173.91107680
> 6.0 -62174.01784370
> 6.5 -62174.07321427
> 7.0 -62174.10037058
> 7.5 -62174.11295891
> 8.0 -62174.11860895
> 8.5 -62174.12108970
> 9.0 -62174.12214200
> 9.5 -62174.12257779
> 10.0 -62174.12275904
> 10.5 -62174.12284153
> press RETURN to continue
>
>
>
> rkmax: | d_E:
> ===============|============== =====
> # rKmax | d-Energy
> 5.0 .34386523000000000000
> 5.5 .19891124000000000000
> 6.0 .10676690000000000000
> 6.5 .05537057000000000000
> 7.0 .02715631000000000000
> 7.5 .01258833000000000000
> 8.0 .00565004000000000000
> 8.5 .00248075000000000000
> 9.0 .00105230000000000000
> 9.5 .00043579000000000000
> 10.0 .00018125000000000000
> 10.5 .00008249000000000000
>
>
> 2. At kpoints 1000K
>
>
> ***********************
> ============================
> rkmax: | Etotal:
> ===========|================
>
> 4.5 -62173.36682006
> 5.0 -62173.71256762
> 5.5 -62173.91087725
> 6.0 -62174.01776660
> 6.5 -62174.07338946
> 7.0 -62174.10035670
> 7.5 -62174.11295604
> 8.0 -62174.11860749
> 8.5 -62174.12108649
> 9.0 -62174.12213685
> press RETURN to continue
>
>
>
> rkmax: | d_E:
> ===============|============== =====
> # rKmax | d-Energy
> 5.0 .34574756000000000000
> 5.5 .19830963000000000000
> 6.0 .10688935000000000000
> 6.5 .05562286000000000000
> 7.0 .02696724000000000000
> 7.5 .01259934000000000000
> 8.0 .00565145000000000000
> 8.5 .00247900000000000000
> 9.0 .00105036000000000000
>
> 3. k-point optimization at RKMax 7
>
>
> ============================
> Kpoint: | Etotal:
> ===========|================
>
> 200 -62174.10034523
> 250 -62174.10038947
> 350 -62174.10037058
> 550 -62174.10034257
> 750 -62174.10038607
> 1000 -62174.10035670
> 1350 -62174.10037359
> 1750 -62174.10037990
> press RETURN to continue
>
>
>
> Kpoint | d_E:
> ==============|=============== ====
> # Kpoint | d-Energy
> 250 .00004424000000000000
> 350 .00001889000000000000
> 550 .00002801000000000000
> 750 .00004350000000000000
> 1000 .00002937000000000000
> 1350 .00001689000000000000
> 1750 .00000631000000000000
>
> Sir, could you please help me what is wrong here and what RKmax and
> k-points I should take for the system LiGaTe2?
>
>
> Regards
> Mr. Shahzad
> PhD Scholar
> GC University, Lahore
> Pakistan
>
>
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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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