Dear Matteo, I met some problem when calculating the XASs with the Xspectra. I tested the example of quartz, and got the consistent result with the published work. Then i moved on to test another example of solid CO2, which has an isotropic symmetry according to C. Brouder's paper. But the X-ray absorption spectrum i got was totally wrong. The first sharp peak which is well-known existing in CO2 was not found. We also tested a single CO2 molecule which is still a clear-cut example. The C atom and the two O atoms are all in the Z axis. So the polarization vectors of (0,0,1) and (1,0,0) are enough for this case. However, we still cannot get the right XAS. To make it easier for you to understand my problem, I attached the input files of this calculation. The GIPAW pseudopotentials i used were downloaded from the website of QE. Thanks a lot for the help.
Best regards, Min Wu 2010-10-17 >From: Matteo Calandra <matteo.calandra at impmc.jussieu.fr> >Reply-To: PWSCF Forum <pw_forum at pwscf.org> >To: pw_forum at pwscf.org >Subject: Re: [Pw_forum] Xspectra calculation (wumindt2) >Date: Mon, 11 Oct 2010 10:08:16 +0200 > >Dear > > I assume you are talking of the dipolar part only. >For the quadrupolar it is substantially more complicate. >The number of independent calculations that you have >to perform to obtain the isotropic cross section (powder) >depends on the point group of the space group >of your crystal. >It is 1 for a cubic or tetraedric crystal, >2 for a uniaxial crystal and it is 3, 4, 6 for a biaxial >(ot trichroic) crystal. >I suggest you read >C. Brouder J. Phys.: Condens. Matter 2 (1990) 701-738 >for more details. > >M. > > >> >> Message: 3 >> Date: Sat, 09 Oct 2010 22:48:53 +0800 >> From: "wumindt2" >> Subject: Re: [Pw_forum] Xspectra calculation >> To: pw_forum at pwscf.org >> Message-ID: >> Content-Type: text/plain; charset="gb2312" >> >> Dear matteo, >> >> Thanks. >> >> For dichroism compound, do we just need the in-plane and the c-axis >> polarization vectors? >> While for trichroism compound, do we need to calculate three different >> polarization vectors? >> Am i right? >> >> Best regards, >> >_______________________________________________ >Pw_forum mailing list >Pw_forum at pwscf.org >http://www.democritos.it/mailman/listinfo/pw_forum > -------------- next part -------------- An embedded and charset-unspecified text was scrubbed... Name: scf.in Url: http://www.democritos.it/pipermail/pw_forum/attachments/20101018/1834f743/attachment.txt -------------- next part -------------- An embedded and charset-unspecified text was scrubbed... Name: CO2-moleculer.xspectra_b.in Url: http://www.democritos.it/pipermail/pw_forum/attachments/20101018/1834f743/attachment.asc -------------- next part -------------- An embedded and charset-unspecified text was scrubbed... Name: CO2-moleculer.xspectra_c.in Url: http://www.democritos.it/pipermail/pw_forum/attachments/20101018/1834f743/attachment-0001.txt