[Pw_forum] Additional informations about XSpectra - Peaks at negative energies?

[Cristian Degli Esposti Boschi]

Thanks to Matteo Calandra for his answers. Regarding the Fermi level,
I have now an additional question based on an example we are dealing 
with. With a preliminar run of XSpectra I see a Fermi energy of
-0.259, so I use this value for ef_r in following calculations.
If I include negative energies (say -30 eV, with respect to this one)
in the input file then in the resulting spectrum I see a *sharp*
peak at about -5 eV.

Now, if levels at negative energy should be all occupied, how can
it result such an evident absorption peak?
Is it related to the "cut_occ_states" option?
By default it is .false. What does this mean exactly?

Thanks again for your help. Cristian


   > (1) is the energy range (xemin,xemax) referred to the Fermi energy
>  > of the preliminar scf calculation?
> 
> No, it is referred to the Fermi level given in input  in the xspectra
> file (input variable ef_r in the input_xspectra namelist. This means
> that if you do not specify the Fermi level then ef_r=0.0 and
> they are referred to the energy zero of the preliminary scf run.
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Cristian Degli Esposti Boschi
CNR, CNISM, Unita' di Ricerca di Bologna, c/o
Dipartimento di Fisica, Universita' di Bologna
viale Berti-Pichat, 6/2, 40127, Bologna, Italia
tel. ++39 051 2095114   fax ++39 051 2095113
e-mail: cristian.degliesposti -AT- unibo.it
web:    http://www.df.unibo.it/fismat/theory
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