[Pw_forum] Is maxirr=N working in phonon calculations?

[Serge Nakhmanson]

Dear Paolo,

Thank you very much for exhaustively answering my questions, even
the one that I did not ask, i.e., if irreps are picked at random,
then what is the purpose of using "maxirr=N"? :))

Your comment on randomness of irrep generation makes sense to me.
I only know a general answer to how it is done -- by induction
from an (Abelian) group of crystal translations -- but am
rusty on particular numerical algorithms. However, I got an
excellent new book by El-Batanouny and Wooten (ISBN 9780521828451),
all the details should be in there.

THX again,

S.

Paolo Giannozzi wrote:
> Serge Nakhmanson wrote:
> 
>> Still the code blasted through all 10 irreps.
> 
> not sure whether the "maxirr" option really works. In the CVS
> version it was replaced by other options that are useful for
> Grid execution (i.e. splitting a long phonon calculation in
> many smaller pieces rto be run on different machines). Its main
> usage was to prevent the code from crashing for cpu time limit
> in a ungraceful way, but option "max_seconds" can do the same.
> 
>> Also, is there any system to which irreps are computed first and
>> which later? Or is this process completely random, i.e. it would
>> be futile to cover a certain frequency window by computing only
>> some, but not all, irreps?
> 
> I don't think this is going to work. Not sure how exactly
> irreps are selected. If no symmetry is present, taht's easy:
> atom 1 component x, y,z, atom 2 component x, y, z and so on.
> In presence of symmetry, the irreps are obtained via a procedure
> in which random matrices are symmetrized, so the order in which
> they are produced is quite unpredictable (also the accuracy of
> this answer is unpredictable, since it is based on vague
> recollections)
> 
> Paolo


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  Serge M. Nakhmanson               phone: (630) 252-5205
  Assistant Scientist                 fax: (630) 252-4798
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