[Pw_forum] SiO2 xanes calculation

[Matteo Calandra]

 >Message: 3
 >Date: Wed, 06 Jul 2011 18:27:57 -0400
 >From: <maxradin at umich.edu>
 >Subject: [Pw_forum] SiO2 xanes calculation
 >To: pw_forum at pwscf.org
 >Message-ID: <d5360c67d8b89e63994a959436f4846e at umich.edu>
 >Content-Type: text/plain; charset="utf-8"
 >
 >Hi,
 >
 >I'm trying to repeat the ultrasoft core-hole calculation of the Si >K-edge
 >in Matteo's paper:
 >
 >"First-principles calculations of x-ray absorption in a scheme
 >based on ultrasoft pseudopotentials: From alpha-quartz to
 >high-Tc  compounds"

 >I haved used the same parameters given in that article (cell size, >cutoff
 >energies, kpoints) but the spectrum that I get does not at all look 
 >right.
 >Is it possible that this discrepancy is due to the choice of
 >pseudopotentials? For the absorbing atom I am using

Dear Max,

   the pseudo you use are correct, however this is not the case for
the k-points in your Xanes calculation. In the paper it is stated
that you need "the Lanczos method was performed
using a centered 3x3x3 k-points grid of the 72
atoms supercell." (see just below Eq. 27).

The second thing is that in an insulator, there is no Fermi level.
Are you sure you're cutting eliminated the occupied states at the right 
energy position ?

Can you try yo see if you reproduce the results of the QE XSpectra 
example directory ?

all the best,

Matteo

-- 
* * * *
Matteo Calandra, Directeur de Recherche (DR2)
Institut de Mineralogie et de Physique des Milieux Condenses de Paris
Universite Pierre et Marie Curie, tour 23, 3eme etage, case 115
4 Place Jussieu, 75252 Paris Cedex 05 France
Tel: +33-1-44 27 52 16       Fax: +33-1-44 27 37 85
http://www.impmc.jussieu.fr/~calandra