[Q-e-developers] gamma_only inconsistency in xspectra

Paolo Giannozzi paolo.giannozzi at uniud.it
Wed Dec 18 22:37:47 CET 2013

Thank you Guido. Do you think that gamma_only should
always be set to .false. in xspectra? or should it
be set to .true. if k=0 is used by xspectra, irrespective
of what it is used by the scf calculation?


On Wed, 2013-12-18 at 12:23 +0100, Guido Fratesi wrote:
> Dear QE developers,
> let me report about xspectra an inconsistency between the flag 
> gamma_only (read from pw save file) and the kpoint mesh, which is read 
> from input.
> That would produce wrong results for NEXAFS calculations of, e.g., 
> molecules in the gas phase, where pw.x is commonly run with gamma_only 
> algorithms, unless the user is especially aware and runs an intermediate 
> pw.x nscf with k-points.
> Comments, results, and scripts for a quick test for C2H2 molecule are 
> attached for your consideration. The problem is also subtle because in 
> small molecules the spectrum may immediately appear as "wrong", but only 
> careful analysis shows that the spectrum is indeed incorrect for larger 
> molecules including several atoms of the same species.
> Best wishes,
> Guido Fratesi
> PS the archive (1.5MB) is available from
> http://www.sendspace.com/file/cy3sr3
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Paolo Giannozzi, Dept. Chemistry&Physics&Environment, 
Univ. Udine, via delle Scienze 208, 33100 Udine, Italy
Phone +39-0432-558216, fax +39-0432-558222 

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