[Wien] Choosing linearisation energies for an insulator

[Peter Blaha]

The choice depends a littel what you want. For scf only the occupied part 
is important, for spectra,.. you may also want accurate energies for the 
conduction bands.
Probably the best method is to add an extra d-LO at a high energy. This 
allows for the best description in a wide energy range.

ii) I'd say: the energy can be always accepted for a low lying state 
("semicore"), because for such states the selection mechanism 
(E-top/E-bottom) always works pretty well.
For high lying states we have some "arbitrary" upper limit, because 
valence states could have an extremely broad E-top/E-bottom and simply 
taking the mean value is not usefull for this case.

> I have a question on how to choose linearisation energies for an insulator
> with a fairly large gap at the Fermi level. I am doing LSDA+U calculations
> on AF-II NiO with a U-value of 8.0 eV. This results in an insulating state
> with a narrow Ni-3d band about 4 eV above the Fermi level. How should I
> choose linearisation energies in this case? Should I base my choice of
> general linearisation energy on the occupied part (up to EF) of the total
> DOS, not paying any attention to the empty part of the band and then add a
> high lying LO for the empty part of the band?
> 
> Another question about linearisation energies:
> In the text by S. Cottenier about DFT and (L)APW-methods, he writes (p.
> 31)that the linearisation energy suggested by the program for a LO can in
> all cases be accepted. What is the reason for this? Is it because their
> energy is so sharply defined that the program will always find a good
> energy by performing a search?
> 
> Any suggestions are welcome!
> 
> Thanks for your replies
> 
> Best regards,
> Thomas Claesson
> 
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                                      P.Blaha
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Peter BLAHA, Inst.f. Materials Chemistry, TU Vienna, A-1060 Vienna
Phone: +43-1-58801-15671             FAX: +43-1-58801-15698
Email: blaha at theochem.tuwien.ac.at    WWW: http://info.tuwien.ac.at/theochem/
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