# [Pw_forum] how to choose ibrav

tian kong thisisasafeaccount at gmail.com
Sat Jun 25 15:49:38 CEST 2011

```yeah, i think you are right. but what really matters is how to set ibrav in
pwscf.

ibrav        structure                   celldm(2)-celldm(6)
<goog_798003211>

6          Tetragonal P (st)               celldm(3)=c/a
7          Tetragonal I (bct)              celldm(3)=c/a

simple tetragonal (p)
====================
v1 = a(1,0,0),  v2 = a(0,1,0),  v3 = a(0,0,c/a)

body centered tetragonal (i)
================================
v1 = (a/2)(1,-1,c/a),  v2 = (a/2)(1,1,c/a),  v3 = (a/2)(-1,-1,c/a).
it seems that: if ibrav=6, then A=B≠C. if ibrav=7, then A=B=C.
but what i need is A≠B=C. i don't know if i can choose ibrav=6 or 7,
and should i need to change the atoms position after i choose ibrav=6
or 7 ?

*>>>>>>>>【this is an email sent by tiankong】*

2011/6/24 GAO Zhe <flux_ray12 at 163.com>

> In your case, this structure must be simple tetragonal or body centered
> tetragonal. Please check your model more carefully from PDF-card or ICSD
> database.
> P.S.: the choice of ibrav depends on the knowledge of crystallography,
> please learn it before you do ab-initio calculation, since symmetry is a
> very important and foundamental thing in this area.
> --
> GAO Zhe
> CMC Lab, MSE, SNU, Seoul, S.Korea
>
> At 2011-06-24 15:25:10，"tian kong" <thisisasafeaccount at gmail.com> wrote:
>
> i have read the help document about INPUT_PW.htm again and again, but since
> i'm a newbie, i still don't know whice one i should choose. can you help me?
> here is the problem:
> A=10, B=C=8, cosAB=cosBC=cosAC=0.
> can you tell me ibrav=?
> thx a lot !!!
> *>>>>>>>>【this is an email sent by tiankong】*
>
>
>
>
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>
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