[Pw_forum] questions on the acoustic sum rule crystal

[stewart at cnf.cornell.edu]

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. 

http://www.people.cornell.edu/pages/das248/ 

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, 

Derek
 

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
> 13-5066   MIT   77 Massachusetts Avenue   Cambridge MA 02139-4307 USA
> tel 617.4522758 fax 2586534 marzari at mit.edu http://quasiamore.mit.edu
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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