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

Paolo Giannozzi giannozz at democritos.it
Wed Nov 5 14:19:10 CET 2008

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

Paolo Giannozzi, Democritos and University of Udine, Italy

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