[Pw_forum] Non-orthogonal modes with dynmat.x at gamma point

[Sridhar Sadasivam]

If you are talking about the vectors printed in the matdyn.modes file, then
yes they are not orthogonal as those are actually eigendisplacements and
not the eigenvectors of the dynamical matrix. But if you multiply the
eigendisplacements of each atom by the square root of the corresponding
atomic mass, then the resulting eigenvectors will be orthogonal.

Hope that helps.
Sridhar


On Wed, Aug 27, 2014 at 8:53 PM, Florian Altvater <altvater at berkeley.edu>
wrote:

> Hi,
> I calculated the phonons for an isolated naphthalene molecule as well as
> naphthalene crystal at q = (0,0,0). After diagonalizing the dynamical
> matrix with dynmat.x and enforcing the appropriate acoustic sum rule -
> "zero-dim" and "crystal" respectively - I get 6 and 3 acoustic modes
> with frequencies of 0 cm^-1. So far so good.
>
> If I use the displacements printed to dynmat.out (filout) and calculate
> the various scalar products of the modes, i.e. c_ij = m_i . m_j, I find
> that they are normalized but not orthogonal (c_ij != 0 for some i != j).
> Some of the overlaps c_ij are as high as 0.75, so it is not just
> numerical noise. By trying to find more information in the source files,
> I discovered that matdyn.x prints two files, flvec and fleig, where
> flvec prints non-orthogonal normalized vectors. So I thought that this
> could be the issue, as it is not clearly stated if dynmat prints
> eigenvectors or normalized modes like flvec. However, multiplying with
> the masses didn't help either.
>
> Is dynmat.x not printing eigenvectors? If it is/should, what could be
> the problem here? How would I debug the problem?
>
> Thanks so much for you help!
> Flo
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