# [Pw_forum] Format of Dynamical Matrix

Paolo Giannozzi paolo.giannozzi at uniud.it
Wed Jun 19 22:37:11 CEST 2013

```On Tue, 2013-06-18 at 12:38 +0430, Mohsen Modaresi wrote:

> 1) The Dynamical Matrix is calculated for two q points in each
> ***.dyn** files.

this means that there are two q points in the star (the set of q-points
that are equivalent by symmetry)

>  But the Diagolnalization is done for only the first q point.

the diagonalization for the second point would give the same results,
since the two points are equivalent by symmetry

> I can not understand what is the necessity of the second q point?

I don't think there is any necessity, but you have all q points (and not
just the irreducible segment) for free.

> 2) I expect a (3Nat*3Nat) for dynamical matrix so the eigen vectro
> which are written in the end of file should be a (1*3*Nat) matrix but
> instead i see a (3*3) matrix, for example (Real+Imaginary),
>   omega( 1) =       7.786434 [THz] =     259.729218 [cm-1]
>
>  (  1.000000  0.000000  0.000087  0.000000 -0.000130  0.000000 )
>  (  0.000344  0.000000  0.000028  0.000000 -0.000144  0.000000 )
>  ( -0.000346  0.000000  0.000095  0.000000 -0.000016  0.000000 )

is this what you see between lines "  omega( 1) =" and  "  omega( 1) ="?
then you have the real and imaginary parts of x, y, z displacements,
or maybe eigenvectors, for the three atoms in the unit cell

> 3) I also worked with Vibra in the Siesta package. In this code the
> positive and negative displacement for atoms in each direction is
> considered but i can not find the same procedure in the ph.x.

see above. For a generic q point, eigenvectors of the dynamical matrix
are complex.

P.

--
Paolo Giannozzi, Dept. Chemistry&Physics&Environment,
Univ. Udine, via delle Scienze 208, 33100 Udine, Italy
Phone +39-0432-558216, fax +39-0432-558222

```

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