# [Pw_forum] the high symmetry line of BCT phonon dispersion band structures

Kondaiah Samudrala konda.physics at gmail.com
Mon Dec 15 20:52:59 CET 2014

```Dear all,

I am still confused with notation of Ibrav=7 in pwscf. The IBRV=7
primitive cell vectors in pwscf are quite different from any other. See
below for two cases of primitive vectors IBRAV=7
*Case1*
For. e.g. In pwscf primitive vectors of IBRV=7 are
crystal axes: (cart. coord. in units of a)
a(1) = (   0.500000  -0.500000   c/a)
a(2) = (   0.500000   0.500000   c/a )
a(3) = (  -0.500000  -0.500000   c/a )
*Case 2*
On the other hand, generally people used as (from published papers)
crystal axes: (cart. coord. in units of a)
a(1) = (  -0.500000  0.500000    c/a)
a(2) = (   0.500000   -0.500000   c/a )
a(3) = (   0.500000   0.500000   -c/a ) .

This variation leads to changes in reciprocal vectors and then IBZ path.
>From Wikipedia (
http://www.sciencedirect.com/science/article/pii/S0927025610002697)
and *http://www.cryst.ehu.es/
<http://www.cryst.ehu.es/> , *I obtained the IBZ path for *case 2.  But, *what
about the IBZ path of *case 1 primitive cell vectors*??  Is both are same
??? But Xcrysden showing something else than regular Gamma, Z, Sigma, P and
N points .

will be appreciated

with regards

S. Appalakondaiah
PhD Student