[Pw_forum] my understanding about ASR

[stewart at cnf.cornell.edu]

I recently studied Kohn anomalies in palladium using Quantum Espresso.  For 
this, I calculated the phonon dispersion with a 8x8x8 q-grid and I also did 
a series of direct calculations along the direction with the Kohn anomaly.  
Overall the agreement was very good.  I found a small deviation between the 
two approaches for small q as you would expect.  The maximum error at the 
Gamma point was 0.07 THz.  For a comparison along the Gamma to X line, see 
Fig 2 (D. A. Stewart, New. J. Phys. 10 043025 (2008)).  Of course, the 
difference you get between ASR results and direct calculations will depend 
strongly on how well relaxed your structure is. 

http://dx.doi.org/10.1088/1367-2630/10/4/043025 

Best regards, 

Derek 


Paolo Giannozzi writes: 

> xwzhang at uestc.edu.cn wrote: 
> 
>> are there any problem that the slope of the phonon around Gamma is 
>> incorrect, because ASR cure the problem of k=0, but what about other 
>> points near it? 
> 
> for phonons at k/=0, the error due to ASR violation seems to be
> usually negligible. I never tried to make calculations with
> very small q, though. 
> 
> Paolo
> -- 
> Paolo Giannozzi, Democritos and University of Udine, Italy
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################################
Derek Stewart, Ph. D.
Scientific Computation Associate
http://www.people.cornell.edu/pages/das248/
250 Duffield Hall
Cornell Nanoscale Facility (CNF)
Ithaca, NY 14853
stewart (at) cnf.cornell.edu
(607) 255-2856