[Pw_forum] questions on the acoustic sum rule crystal

stewart at cnf.cornell.edu stewart at cnf.cornell.edu
Mon Mar 10 14:47:46 CET 2008

Hi Eduardo, 

If you are interested in learning more about the Lagrangian approach for the 
acoustic sum rule, the full reference for the paper is: 

N. Mingo, D. A. Stewart, D. A. Broido, and D. Srivastava, “Phonon 
transmission through defects in nanotubes from first principles”, Physical 
Review B 77, 033418 (2008) 

I also have a local copy of it stored on my webpage. 


We developed this approach while working on some thermal transport 
calculations for nanotubes using real space force constants from the Siesta 
code.  It should be able to handle fairly large systems.  I think the 
largest we have used it on so far is a 7 unit cell (6,0) nanotube. 

Best regards, 


Nicola Marzari writes: 

> Eduardo Ariel Menendez Proupin wrote:
>> Hi, 
>> Question 1. This question is about the Acoustic Sum Rule in phonon 
>> calculations. Is there a reference to learn about the option 
>> zasr='crystal'?
>> Is 'crystal' always better than 'simple' ?
> I think "crystal" was implemented by Nicolas Mounet - a MSc student here
> in our group - and was based on the idea that the IFCs are a vector in
> a multi-dimensional space, and you should take the projection of these 
> onto the hypersurface where the ASR are satisfied. I'd think it's
> better, in that it imposed simultaneously all constraints in the
> least disruptive way, if oyu are happy with the cartesian metrics
> for the distance; it might take a lot of memory or time in really large
> systems. 
> It's described in his thesis - I'd be happy to send it. We never 
> published it, but maybe it's time - a recent PRB by Mingo also discusses 
> it, and introduces another alternative based on Lagrangian multipliers.
>> Question 2. Consider the calculation of the phonon DOS, as in example 
>> 06. The ASR can be imposed in the run of q2r and/or in the run of 
>> matdyn, let's say
>> There are four combinations of zasr-asr in q2r an matdyn
>>         q2r          matdyn
>>  1       no         no
>>  2       no         crystal
>>  3      crystal    no
>>  4      crystal    crystal 
>> Should  there be  differences in the final DOS in the combinations 2, 3, 
>> and 4?
> I'd like to know myself -but last time I looked into the q2r and
> maydyn was 16 years ago :-( . Maybe you could report any differences
> (rather than in the DOS, I'd look at low energy acoustic phonons, both
> at Gamma but especially close to gamma, but not really there). 
> 					nicola 
> ---------------------------------------------------------------------
> Prof Nicola Marzari   Department of Materials Science and Engineering
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Derek Stewart, Ph. D.
Scientific Computation Associate
250 Duffield Hall
Cornell Nanoscale Facility (CNF)
Ithaca, NY 14853
stewart (at) cnf.cornell.edu
(607) 255-2856

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