# [Pw_forum] Mismatch in symmetry operations for diamond

Mon Sep 19 13:37:10 CEST 2016

```Hi Paolo,

I was attempting to extract the symmetries in an EPW routine in order to simplify the calculations. I used a loop ns=1,nrot and inside this loop, I printed sr(:,:,2). Perhaps I should have looped over nsym instead of nrot. I will check to see if this makes a difference.

Thanks,

Vahid

On Sep 19, 2016, at 2:57 AM, Paolo Giannozzi <p.giannozzi at gmail.com<mailto:p.giannozzi at gmail.com>> wrote:

What is printed on output is exactly sr(:,:,isym), with isym running over symmetries. Where and how did you print sr(:,:,2)? and what about all other symmetries?

Paolo

On Mon, Sep 19, 2016 at 12:28 AM, Vahid Askarpour <vh261281 at dal.ca<mailto:vh261281 at dal.ca>> wrote:
Dear QE Users,

When doing relaxation on diamond, one of the symmetry operations identified by QE-5.4.0 is the following:

isym =  2     180 deg rotation - cart. axis [0,0,1]

cryst.   s( 2) = (     0          1         -1      )
(     1          0         -1      )
(     0          0         -1      )

cart.    s( 2) = ( -1.0000000  0.0000000  0.0000000 )
(  0.0000000 -1.0000000  0.0000000 )
(  0.0000000  0.0000000  1.0000000 )

However, when I print out sr(:,:,2) for this structure (isym=2), I get :

1.00000000000000                0.000000000000000E+000   0.000000000000000E+000
0.000000000000000E+000  -1.00000000000000                0.000000000000000E+000
0.000000000000000E+000    0.000000000000000E+000   1.00000000000000

Since the sr matrix prints the cartesian rotation matrix, there seems to be a mismatch between the sr(1,1) elements. The other elements are consistent.

Is this a bug or am I missing another operation embedded in the sr matrix?

Thank you,

Vahid

Department of Physics and Atmospheric Science
Dalhousie University,

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--
Paolo Giannozzi, Dip. Scienze Matematiche Informatiche e Fisiche,
Univ. Udine, via delle Scienze 208, 33100 Udine, Italy
Phone +39-0432-558216, fax +39-0432-558222

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