[Wien] Calculation of Ueff

[karima Physique]

Thank you very much for your detailed response.

2017-03-28 3:48 GMT+02:00 Gavin Abo <gsabo at crimson.ua.edu>:

> The NiO example [1] with 1 k-point gave about 6 eV with the NiO_+.5-1
> calculation taking about 36 cycles [2,3].  N.B. [4], this is with 2.00 and
> not 20.3 in case.in1.  I believe the 20.3 in the paper may be a
> typographical error. At the bottom of [1], there is the statement:
>
> Usually, it is better to just set the d energy 2-4 Ry above the Fermi
> level.
>
> The Fermi level is not known when starting the calculation, but a small
> value of about 0 is likely a reasonable assumption.  So let Fermi level =
> 0.  Taking the lower value of 2 Ry from the statement above.  So took 2.00
> for case.in1.  I think the Fermi level obtained after the calculation was
> about 0.5. If you round that down, it becomes zero.  So it seems the 0 was
> likely an okay starting assumption.
>
> I suspect 1 k-point and 5 RKmax wouldn't be used if it was a proper
> calculation, but the paper is an example such that it was likely chosen for
> speed [5].
>
> For example, it looks like 100 k-points and 5.7 RKmax (instead of 1
> k-point and 5 RKmax) were used in G. K. H. Madsen and P. Novak calculation
> for Fe3O4 [6].
>
> Keep in mind that the Ueff values obtained from the Constrained method are
> known to be of questionable accuracy [7].
>
> Rather than your two choices below, it is better to do convergence tests
> [8-12].
>
> [1] http://susi.theochem.tuwien.ac.at/reg_user/textbooks/Constraint_U.pdf
> [2] http://www.mail-archive.com/wien@zeus.theochem.tuwien.ac.
> at/msg14460.html
> [3] http://wien2k-algerien1970.blogspot.com/2016/08/how-to-
> calculate-u-parameter-in-nickel.html
> [4] https://en.wikipedia.org/wiki/Nota_bene
> [5] http://www.mail-archive.com/wien@zeus.theochem.tuwien.ac.
> at/msg15593.html
> [6] https://arxiv.org/abs/cond-mat/0412560v1
> [7] http://www.mail-archive.com/wien@zeus.theochem.tuwien.ac.
> at/msg12429.html
> [8] http://www.mail-archive.com/wien@zeus.theochem.tuwien.ac.
> at/msg15596.html
> [9] http://wien2k-algerien1970.blogspot.com/2016/08/kpoint-
> convergence-test.html
> [10] https://www.beilstein-journals.org/bjnano/content/
> supplementary/2190-4286-2-45-S1.pdf
> [11] http://www.mail-archive.com/wien%40zeus.theochem.tuwien.
> ac.at/msg01700.html
> [12] http://www.mail-archive.com/wien%40zeus.theochem.tuwien.
> ac.at/msg08186.html
>
> On 3/27/2017 9:50 AM, karima Physique wrote:
>
> Thank you for your answer but i I noticed that Ueff is very sensitive with
> the change of RKmax and Kpoint it is for this I evoked this subject abd
>  for example
> For K = 1 and RKmax 5 i found Ueff = 3.6 eV
> But For K = 100 Points and RKmax 8.5 i found Ueff = 5.4 eV
>
> 5.4 and 3.6 are relatively far
>
> What I really ask is that the choice of one point is it mandatory? (as is
> indicated in the paper of G. K. H. Madsen and P. Novak) or else I have to
> force these parameters (a large number of Kpoint and rkmax> 7) which of
> these two choices is good
>
>
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