[CP2K-user] [CP2K:11881] DFT+U with Ti and O

[kazimieras tamoliunas]

Thank you!!

On Mon, Jun 17, 2019, 17:27 Krack Matthias (PSI) <matthi... at psi.ch>
wrote:

> Hi Kazimieras
>
>
>
> You will get that warning whenever you have more than six 2p electrons for
> O or two for the O 2s, though I assume that you want to have a Hubbard U
> correction for the Ti 3d states alone or for both Ti 3d and O 2p states.
> Other choices might not made much sense.
>
> Mulliken is known to give orbital occupations which can be slightly larger
> than the limit of 2l+1 (or 4l+2 for closed shell) for some cases, e.g. more
> than 10 d electrons for Zn. You can ignore that warning if the occupation
> is only slightly larger than expected. There is a print key
> https://manual.cp2k.org/trunk/CP2K_INPUT/FORCE_EVAL/DFT/PRINT/PLUS_U.html
> which prints the occupations of the orbitals for which a U value greater
> zero has been assigned in the input.
>
>
>
> Matthias
>
>
>
> *From:* cp... at googlegroups.com <cp... at googlegroups.com> *On Behalf Of *kazimieras
> tamoliunas
> *Sent:* Montag, 17. Juni 2019 09:46
> *To:* cp2k <cp... at googlegroups.com>
> *Subject:* [CP2K:11881] DFT+U with Ti and O
>
>
>
> Hello,
>
>  i'm calculating Na(+1)Ti2(+4)(PO4)3(-3) using DFT+U method and the
> system is quite big ( 108 atoms, calculating 2x2x1, so 432 atoms in total)
> and i'm trying to fit the U parameter. Now i'm using U for both Ti and O
> (obviously Ti d orbitals). However, what's less obvious is what kind of
> orbitals should i apply the U correction to, regarding oxygen? Whenever i
> apply L=0 or L=1 ( p sounds reasonable to me) it prints out a following
> message:
>
>
>
> *** 04:19:11 WARNING in dft_plus_u:mulliken :: DFT+U energy contibution ***
>  *** is negative possibly due to unphysical Mulliken charges. Check your
> ***
>  *** input, if this warning persists or try a different method!
>
>
>
> Now when i set L=2 for O, the warning disappears and i get a great
> convergence.
>
> That i do like, however, i cannot understand how this method works. I
> suppose i have oxygen mostly -2, therefore it should have it's 2p fully
> filled. From my point of view, if i want to localise the electron i should
> think about 3s or 2p, but certainly not 3d orbital. Can somebody help me
> with that?
>
> Appreciate any help, comments or possible literature from the ones
> familiar with the problem!
>
>
>
> PS. i know that these oxidation states are not correct and you cannot
> precisely have them in a periodic system. However, i suppose, that DFT+U
> method is used for certain electron localisation, therefore, i feel that
> they provide some ground to rely upon. Correct me if i'm mistaken!!
>
>
>
> Regards,
>
> Kazimieras
>
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