[Pw_forum] xspectra calculation

[jiayudai]

Dear Matteo,

Do you think what's the difference between the method in XSpectra code and the method in Abinit (see the ref: http://prl.aps.org/abstract/PRL/v101/i15/e155001, http://prb.aps.org/abstract/PRB/v80/i6/e064110). I think the treatment is very similar, but they consider the Fermi-Dirac distribution for electrons. It seems that they also cut the occupied states when they calculate the xanes. So, do you think if we consider the Fermi distribution of electrons, this model can be used for metals?

Regards.

Jiayu

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Message: 5
Date: Wed, 20 Oct 2010 17:13:39 +0200
From: Matteo Calandra 
Subject: Re: [Pw_forum] xspectra calculation
To: pw_forum at pwscf.org
Message-ID: <4CBF0723.9030508 at impmc.jussieu.fr>
Content-Type: text/plain; charset=ISO-8859-1; format=flowed

>Dear Matteo,

>So when we just do the dipolar part, we don't need to care about the
>k vector, right?

yes, it is not used.

>Besides, in order to compare with an experimental spectrum, is it necessary to cut
>the occupied state below Fermi energy level within our Xspectra calculation ?
>In that case, we should set "cut_occ_states" = .true. and 
>"ef_r" equal to the fermi energy we got in the scf calculation. Is it?

Yes. However if you have a small gap insulator, introduction of a 
core-hole can lead to a metallic system (close the gap). In this case it is
not clear where to cut. Actually in this case the static core-hole 
approximation is probably incorrect.
For metals it is even worst.

M.

Best regards,