Re: Position of the Ef in LDOS

["John J. Rehr" <jjr@leonardo.phys.washington.edu>]

 Dear Sergio,

  We would have to see a feff.inp to say for sure. But here are some
possibilities:

 a) the SCF loop hasn't completely converged
 b) you don't impose stoichiometry in the potentials, so 
    the potentials are not completely neutral - it's important
    to do add stoichiometry 
 c) the cluster is not large enough
 d) the basis is too small, so you miss some occupied states
 e) there is enough "leakage" to unoccupied states that
    the calculation is off. It's not unusual to be off by 1-2 eV.

  In any case, a simple fix is to move the E_0 with the
EXCHANGE card to mid gap.

  Cheers,
  John
 
> I would like to mention that I have found the same problem that Maurizio 
> has mentioned. In my case was for MO and MO2 oxides. My additional problem 
> is that my compounds has a band gap but the Fermi level is not falling 
> there (I have found states just on the fermi level as maurizio has 
> mentioned).
> 
> Thank you for your help.
> 
> Sergio.
> 
> On May 22 2003, Maurizio Mattesini wrote:
> 
> > Dear feffusers
> > 
> > after having plotted the L3-edge (XAS) for a M_{2}S system I've been 
> > trying to assign the peaks on the spectra by looking at the local DOS. 
> > Everything looks fine except the position of the Fermi energy. First I've 
> > plotted the partial DOS and then I have scaled the states with the value 
> > of the Fermi energy given at the top of the ldosNN.dat file. However, 
> > despite this the d-states (the states that are contributing most to the 
> > L-edge) still appear below the Ef, as if they were fully occupied. This 
> > is a bit strange since XAS should be very similar to the unoccupied DOS. 
> > I should also mention that the DOS is made of only one single peak (metal 
> > d-states) which has almost the same shape of the calculated XAS spectra. 
> > To me there is no doubt that the XAS refers to these d-states. I have 
> > also checked the xmu.dat file and there I saw that the L-edge start 
> > effectively from an energy around -10 eV, pointing therefore to the 
> > d-states located just below the Ef.
> > 
> > Now, my question is: when plotting the DOS one has to account for the Ef 
> > value given at the top of the ldosNN.dat file but it is evident that this 
> > is not enough to get the "real DOS". Is there any way to place the Ef in 
> > the DOS plot correctly? Should I further scale my DOS with the value of 
> > the threshold energy of the L-edge?
> > 
> > Any hints will be highly appreciated.
> > Thank you very much.
> > 
> > Maurizio
> >  
> 
> -- 
> Dr. M.S.Moreno
> University of Cambridge
> Department of Materials Science and Metallurgy
> Pembroke Street
> Cambridge CB2 3QZ
>