[Pw_forum] phonon modes assignment and others

[Paolo Giannozzi]

On Saturday 07 January 2006 17:15, W. YU wrote:

> 1. Is there an easy or not so easy way to assign the
> different modes from the phonon calculation results to 
> the various irreducible representations?  

no easy way, only not-so-easy ways. Once upon a time I wrote 
a small code that did exactly that for molecular fullerene C60, 
but it is a special case in which most modes can be identified 
by their parity and degeneracy; the remaining ones by some 
simple tricks. I vaguely remember that somebody sent a pointer
to some general code for irrep calculation, but I couldn't find the 
message.

> 2. When I use dynmat.x to extract normal mode eigen
> vectors for the Gamma point, the results seems to be
> different from those given by the phonon output.

dynmat.x writes the eigendisplacements (u = v/M^{-1/2}), 
not the eigenmodes (v)

> 3. When doing phonon calculation, we are not using
> supercell, but I know q2r does account for the
> interactions among different neighbours. Then is it
> possible for me to know exactly up to which nearest
> neighbour is included in the calculation?

your q-point grid is equivalent to (i.e. it is the reciprocal
lattice of) a supercell in R-space. The range of neighbours
included in the calculation depends on the size of this 
supercell

Paolo

-- 
Paolo Giannozzi             e-mail:  giannozz at nest.sns.it
Scuola Normale Superiore    Phone:   +39/050-509876, Fax:-563513 
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