[Wien] Crystal field splitting in empty 3d band of Fe2O3

[Hua Wu]

Dear Y. Ding,

 For the material Fe2O3 having the formal high-spin Fe3+ and a closed 
up-spin shell, I think LDA (when giving an insulating solution) or LDA+U
partial d-DOS can well show the t2g-eg (if being eigenorbitals) crystal field 
splitting. 

Just a note: have you worked with a hexagonal lattice coordinate or a local 
octahedral coordinate ?  May the short Fe-Fe pair or a trigonal field distort 
too much the crystal field level diagram ?

best regards -- H. Wu
    
On Thursday 17 September 2009 07:51, Pavel Novak wrote:
>  Dear Yang Ding,
>
> yesterday I forgot third point, which perhaps could give answer to your
> question. If U is chosen such that it put d-states close to the oxygen p-
> states, hybridization increases and it shifts the d-levels down if Ed<Ep,
> or up if Ed>Ep.
> Regards Pavel
>
> On Wed, 16 Sep 2009, Pavel Novak wrote:
> > Dear Yang Ding,
> >
> > care is needed when estimating the crystal field splitting from the LDA+U
> > calculation using the DOS. There are two reasons for it. First, the LDA+U
> > lower the energy of more occupied states and increase the energy of less
> > occupied states. Even if the bands are above Fermi energy, they contain
> > nonzero fraction of electrons (cf :QTL in scf file), which is different
> > for eg and t2g states, hence LDA+U distorts the splitting. Second, the
> > selfinteraction of the d-electrons is present, again distorting the
> > crystal field splitting.
> >
> > Regards
> > Pavel Novak
> >
> > On Tue, 15 Sep 2009, Yang Ding wrote:
> > > Dear WIEN2k  users,
> > >
> > > I am really new to WIEN2k, and wondering if you could give your advice
> > > and experience on following question concerning the crystal filed
> > > splitting calculated from WIEN2k.
> > >
> > > In order to understand if the pre-edge splitting appearing in the Fe
> > > K-edge spectra (1s-4p transition) measured by emission-XANES on Fe2O3
> > > [Groot et al. J. Phys.: Condens. Matter 21 (2009) 104207
> > > <http://www.iop.org/EJ/abstract/0953-8984/21/10/104207/>], is linked to
> > > crystal-filed splitting in 3d empty band. We did a very preliminary
> > > ground state calculation using WIEN2k based on GGA+U (and LSDA+U) with
> > > U = 4 eV structure to check the crystal field splitting in empty d band
> > > above Fermi level.
> > >
> > > As a result, we found that above 2-6 eV above Fermi level, the energy
> > > of t2g is higher than that of eg. This result is similar to what
> > > reported by Rollsman et al (PHYSICAL REVIEW B 69, 165107 (2004)
> > > <http://prola.aps.org/abstract/PRB/v69/i16/e165107>) on Fe2O3. In his
> > > calculation (GGA/LSDA+U , U= 4eV), the energy of t2g is also higher
> > > than that of eg. So my question is why the t2g and eg are reversed in
> > > DFT, but the Multiplet calculation gives contradictory results (i.e
> > > from Groot et al.).
> > >
> > > I noticed that  Glatzel et al (PHYSICAL REVIEW B 77, 115133 (2008)
> > > <http://prola.aps.org/abstract/PRB/v69/i16/e165107>) reported that they
> > > obtained the "right" crystal field splitting using (LDA+U, U=6 eV) from
> > > WIEN2k.   So we wonder if we might missed something in the
> > > calculations?
> > >
> > > Thanks  in advance for your help,