[CP2K:9425] DFT+U Calculation

[Sudhir K. Sahoo]

Dear Matthias,

You are correct. The occupation of d-orbital is larger than 10 when large
value of U is used,
and occupation for d-orbital is less than 10 only when value of U is very
low (=1 eV).
Do you think, this small value of U would be sufficient.

Thanks,
Sudhir



On Mon, Sep 18, 2017 at 5:03 PM, Krack Matthias (PSI) <matthia... at psi.ch
> wrote:

> Dear Sudhir
>
>
>
> You enforce a smearing of the projected d orbital occupations until an SCF
> convergence threshold of 1.0E-8 is reached (and for at least 10 SCF
> iteration steps). This will imply that the occupation constraint is never
> released during the SCF iteration loop unless your SCF convergence limit is
> even smaller than 1.0E-8 (well, you possibly never get there). That is also
> most likely the reason for the persistence of the warning. I suggest to
> comment/remove the EPS_SCF 1.0E-8 line. After 10 SCF iteration steps the
> SCF cycle will then evolve without occupation constraint. You may even set
> “&ENFORCE_OCCUPATION off” and drop the occupation constraint completely,
> since you do not want to enforce any specific d orbital occupation pattern
> obviously as you are smearing over all d orbitals anyway. You may also drop
> the U_RAMPING unless that is crucially needed to achieve convergence.
>
>
>
> Best regards
>
>
>
> Matthias
>
>
>
> *From:* cp... at googlegroups.com [mailto:cp... at googlegroups.com] *On Behalf
> Of *Sudhir K. Sahoo
> *Sent:* 18 September 2017 16:40
> *To:* cp... at googlegroups.com
> *Subject:* Re: [CP2K:9424] DFT+U Calculation
>
>
> Dear Matthias,
>
> Many thanks for your reply and explanation. I have done one calculation
> with a lower value of U (2 eV), but got the same warning.
>
> Below is the input for DFT+U.
>
>        &DFT_PLUS_U  T
>          L  2
>          U_MINUS_J [eV] 2.0
>          INIT_U_RAMPING_EACH_SCF
>          U_RAMPING [eV] 0.10
>          &ENFORCE_OCCUPATION
>             EPS_SCF 1.0E-8
>             MAX_SCF 10
>             ORBITALS -2 -1 0 1 2
>             SMEAR
>          &END ENFORCE_OCCUPATION
>        &END DFT_PLUS_U
>
> I will give a try to print the detail orbital occupation.
>
> Thanks,
>
> Sudhir
>
>
>
>
>
> On Mon, Sep 18, 2017 at 4:03 PM, Krack Matthias (PSI) <
> matthia... at psi.ch> wrote:
>
> Dear Sudhir
>
>
>
> This warning pops up when the Mulliken population analysis (MPA) returns
> an orbital occupation larger than the maximum number of electrons allowed
> for the actual l value specified in the +U section, e.g. more than 10
> electrons are assigned by the MPA to the Cu 3d (l=2) orbitals. This can be
> an indicator for a too large U value enforcing a too high on-site
> localisation. Please, note that the U(eff) values successfully employed by
> PW codes are not transferable to CP2K. The corresponding U values for CP2K
> are usually smaller, roughly by a factor of two, e.g. with respect to their
> impact on the band gap. You can specifically print the detailed orbital
> occupations of the +U atoms using this CP2K print key
> <https://manual.cp2k.org/cp2k-4_1-branch/CP2K_INPUT/FORCE_EVAL/DFT/PRINT/PLUS_U.html>
> with “QS_SCF 1” in its &EACH section. The warning appears easily for
> systems like ZnO with a 3d10 configuration when the MPA assigns for
> instance 10.04 electrons to the Zn 3d orbitals of some Zn atoms. The
> warning can then be ignored possibly for such spurious violations of the
> maximum orbital occupation. It is up to the user eventually to decide, if
> the obtained results are still physically meaningful. There is always the
> option to employ another method when DFT+U troubles, e.g. DFT with hybrid
> functionals.
>
>
>
> Best regards
>
>
>
> Matthias
>
>
>
> *From:* cp... at googlegroups.com [mailto:cp... at googlegroups.com] *On Behalf
> Of *sudhir kumar Sahoo
> *Sent:* 18 September 2017 15:03
> *To:* cp2k
> *Subject:* [CP2K:9422] DFT+U Calculation
>
>
>
> Dear cp2k users,
>
> I am using DFT+U method for modelling CuInSe2 (U=5.0 eV for 3d electrons
> of Cu), particularly, using Mulliken method as implemented in cp2k program.
> However, a warning is repeatedly written in the output file.
>
>  *** WARNING in dft_plus_u.F:1455 :: DFT+U energy contibution is negative
> ***
>  *** possibly due to unphysical Mulliken charges. Check your input, if
> ***
>  *** this warning persists or try a different method!
> ***
>
> After reading the cp2k google group discussion, I have tried to perform
> DFT+U calculations as explained below,
> but each time I got the same warning in the output file.
>
> 1) Restarting the calculation U=5 eV, from an optimized wavefunction
> obtained from U=0 eV.
> 2) Point 1 + u_ramping option
> 3) Point 2 + &enforce_occupation
>
> Can someone please help me in this.
>
> Thanking You,
> Sudhir
>
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> --
>
> Sudhir Kumar Sahoo
> C/O - Prof. Thomas D. Kühne
> Post-doc Researcher
>
> Department of Chemistry
>
> University of Paderborn
>
>
>
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-- 
Sudhir Kumar Sahoo
C/O - Prof. Thomas D. Kühne
Post-doc Researcher
Department of Chemistry
University of Paderborn
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