[Pw_forum] how to choose ibrav

[Huiqun Zhou]

Hi, 

It's your own responsibility to make clear what crystal class your system belongs to.
Do you know the symbol of space group of your system? For your case, if it's Pxxx, 
the system should be simple tetragonal (ibrav=6), if it's Ixxx, it should be base centered 
tetragonal (ibrav=7).


zhou huiqun
@earth sciences, nanjing university, china

  ----- Original Message ----- 
  From: tian kong 
  To: PWSCF Forum 
  Sent: Saturday, June 25, 2011 9:49 PM
  Subject: Re: [Pw_forum] how to choose ibrav


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

  ibrav        structure                   celldm(2)-celldm(6)

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